Magnetic sensor device

ABSTRACT

A magnetic sensor device includes a magnetic sensor, and a soft magnetic structure disposed near the magnetic sensor. The magnetic sensor and the soft magnetic structure are configured so that when an external magnetic field including a detection-target magnetic field is applied to the magnetic sensor, the external magnetic field is also applied to the soft magnetic structure, and when the soft magnetic structure has a magnetization, a magnetic field based on the magnetization of the soft magnetic structure is applied to the magnetic sensor. The soft magnetic structure has a stripe domain structure.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic sensor device including amagnetic sensor and a soft magnetic structure.

2. Description of the Related Art

Magnetic sensors have been used for a variety of purposes. Some knownmagnetic sensors use a plurality of magnetic detection elements providedon a substrate. Examples of the magnetic detection elements includemagnetoresistive elements.

US 2012/0200292 A1 discloses a geomagnetic sensor in which an X-axismagnetic sensor, a Y-axis magnetic sensor, and a Z-axis magnetic sensorare provided on a base. In this geomagnetic sensor, the Z-axis magneticsensor includes magnetoresistive elements and soft magnetic bodies. Thesoft magnetic bodies convert vertical magnetic field components, whichare in a direction parallel to the Z-axis, into horizontal magneticfield components in a direction perpendicular to the Z-axis, and supplythe horizontal magnetic field components to the magnetoresistiveelements.

JP H07-249518A describes a magnetic head including a soft magnetic thinfilm having a stripe domain structure. JP H07-249518A describes thateven with a magnetic head including a soft magnetic thin film that iseasy to exhibit uniaxial anisotropy within the film plane, a highradio-frequency permeability in all directions can be achieved byemploying the stripe domain structure for the soft magnetic thin film.

Now, consider a magnetic sensor device including a first magnetic sensorfor detecting a horizontal magnetic field component and a soft magneticstructure disposed horizontally close to the first magnetic sensor. Thesoft magnetic structure is formed of a soft magnetic material. The softmagnetic structure is not a component of the first magnetic sensor. Anexample of such a magnetic sensor device is the aforementionedgeomagnetic sensor described in US 2012/0200292 A1. In the geomagneticsensor disclosed therein, the X-axis magnetic sensor and the Y-axismagnetic sensor correspond to the first magnetic sensor, and the softmagnetic bodies of the Z-axis magnetic sensor correspond to the softmagnetic structure.

The foregoing magnetic sensor device has a problem that if the softmagnetic structure has a magnetic hysteresis characteristic, themagnetic hysteresis characteristic causes the detection value of thefirst magnetic sensor to exhibit a hysteresis characteristic, therebycausing a drop in the detection accuracy of the first magnetic sensor.This will be described in detail below. If the soft magnetic structurehas a magnetic hysteresis characteristic, once the soft magneticstructure has been magnetized by an external magnetic field, a certainamount of magnetization remains in the soft magnetic structure evenafter the external magnetic field becomes zero. A magnetic field basedon such magnetization is applied to the first magnetic sensor. As aresult, the detection value of the first magnetic sensor at a zeroexternal magnetic field differs from the ideal value. The direction andmagnitude of the magnetization remaining in the soft magnetic structureat a zero external magnetic field vary depending on the direction andmagnitude of the external magnetic field before the external magneticfield becomes zero. The detection value of the first magnetic sensor ata zero external magnetic field thus varies depending on the directionand magnitude of the external magnetic field before the externalmagnetic field becomes zero. This gives the detection value of the firstmagnetic sensor a hysteresis characteristic.

To improve the detection accuracy of the first magnetic sensor of theforegoing magnetic sensor device, no consideration has heretofore beengiven to optimizing the magnetic characteristics of the soft magneticstructure which is not a component of the first magnetic sensor.

As discussed above, JP H07-249518A describes a magnetic head including asoft magnetic thin film having a stripe domain structure. The softmagnetic thin film is a component of the magnetic head. Thus, therelationship between the magnetic head and the soft magnetic thin filmin JP H07-249518A differs from the relationship between the firstmagnetic sensor and the soft magnetic structure in the foregoingmagnetic sensor device.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a magnetic sensordevice that can prevent a magnetic sensor from being degraded in thedetection accuracy due to a magnetic hysteresis characteristic of a softmagnetic structure disposed near the magnetic sensor.

A magnetic sensor device of the present invention includes a firstmagnetic sensor for generating a first detection value corresponding toa first detection-target magnetic field, and a soft magnetic structureformed of a soft magnetic material. The first magnetic sensor and thesoft magnetic structure are configured so that when the soft magneticstructure has a magnetization, a magnetic field based on themagnetization of the soft magnetic structure is applied to the firstmagnetic sensor. At least part of the soft magnetic structure has astripe domain structure.

The magnetic sensor device of the present invention may further includea second magnetic sensor for generating a second detection valuecorresponding to a second detection-target magnetic field. In such acase, the first detection-target magnetic field may be a component of anexternal magnetic field and in a direction parallel to a firstdirection, and the second detection-target magnetic field may be acomponent of the external magnetic field and in a direction parallel toa second direction. The soft magnetic structure may be arranged not tooverlap the first magnetic sensor but to overlap the second magneticsensor as viewed in a direction parallel to the second direction.

The soft magnetic structure may include a magnetic field converterconfigured to receive the second detection-target magnetic field andoutput an output magnetic field component that is in a directionintersecting the second direction. The output magnetic field componenthas a strength having a correspondence with a strength of the seconddetection-target magnetic field. The second magnetic sensor may beconfigured to detect the strength of the output magnetic fieldcomponent. The soft magnetic structure may further include at least onesoft magnetic layer. The first direction and the second direction may beorthogonal to each other. Note that in the present invention, the“output magnetic field component” corresponds to a component of anoutput magnetic field vector, which is a vector representation of anoutput magnetic field outputted by the magnetic field converter,obtained by projecting the output magnetic field vector in a certaindirection. To “output an output magnetic field component” is based onthe fact that the output magnetic field contains an output magneticfield component which is a component in a certain direction.

When the magnetic sensor device of the present invention includes thesecond magnetic sensor, the magnetic sensor device may further include athird magnetic sensor for generating a third detection valuecorresponding to a third detection-target magnetic field. The thirddetection-target magnetic field may be a component of the externalmagnetic field and in a direction parallel to a third direction. Thethird magnetic sensor and the soft magnetic structure may be configuredso that when the soft magnetic structure has a magnetization, a magneticfield based on the magnetization of the soft magnetic structure isapplied to the third magnetic sensor. In such a case, the first to thirddirections may be orthogonal to each other.

In the magnetic sensor device of the present invention, the firstmagnetic sensor and the soft magnetic structure may be configured sothat when an external magnetic field including the firstdetection-target magnetic field is applied to the first magnetic sensor,the external magnetic field is also applied to the soft magneticstructure. The external magnetic field may have a strength varyingwithin a predetermined variable range.

In an orthogonal coordinate system having two orthogonal axes forrepresenting an applied field strength and a magnetization-correspondingvalue, coordinates representing the applied field strength and themagnetization-corresponding value may move within a region enclosed by amajor loop as the strength of the external magnetic field varies withinthe predetermined variable range. Here, the applied field strength isthe strength of a magnetic field applied to the soft magnetic structurein a direction parallel to a predetermined direction, and themagnetization-corresponding value is a value corresponding to acomponent of the magnetization of the soft magnetic structure, thecomponent being in the direction parallel to the predetermineddirection. The major loop is, among loops traced by a path of thecoordinates representing the applied field strength and themagnetization-corresponding value in the orthogonal coordinate system asthe applied field strength is varied, a loop that is the largest interms of area of the region enclosed by the loop. The predeterminedvariable range may be a range not more than 21.6 Oe in absolute value.Note that a magnetic flux density corresponding to a magnetic fieldhaving a strength of 1 Oe is 0.1 mT.

According to the magnetic sensor device of the present invention, atleast part of the soft magnetic structure has a stripe domain structure.This makes it possible to prevent the first magnetic sensor from beingdegraded in the detection accuracy due to a magnetic hysteresischaracteristic of the soft magnetic structure.

Other and further objects, features and advantages of the presentinvention will appear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a schematic configuration of a magneticsensor device according to an embodiment of the invention.

FIG. 2 is a circuit diagram showing an example circuit configuration ofthe magnetic sensor device according to the embodiment of the invention.

FIG. 3 is a perspective view of a magnetoresistive element of theembodiment of the invention.

FIG. 4 is a perspective view of part of a resistor section of theembodiment of the invention.

FIG. 5 is an explanatory diagram showing an example configuration of amagnetic field converter of the embodiment of the invention.

FIG. 6 is a cross-sectional view showing respective portions of threemagnetic sensors and a soft magnetic structure of the embodiment of theinvention.

FIG. 7 is an explanatory diagram for qualitatively explaining thecharacteristics of a hysteresis loop of the soft magnetic structure andthe behavior of a stripe domain structure in the embodiment of theinvention.

FIG. 8 is a characteristic chart showing an example of major and minorloops in a first case.

FIG. 9 is a characteristic chart showing a portion of FIG. 8 on anenlarged scale.

FIG. 10 is a characteristic chart showing an example of major and minorloops in a second case.

FIG. 11 is a characteristic chart showing a portion of FIG. 10 on anenlarged scale.

FIG. 12 is a characteristic chart showing an example of major and minorloops in a third case.

FIG. 13 is a characteristic chart showing a portion of FIG. 12 on anenlarged scale.

FIG. 14 is an explanatory diagram showing an initial stripe domainstructure in the third case.

FIG. 15 is an explanatory diagram showing the stripe domain structurewhen an applied field strength is zero in the third case.

FIG. 16 is an explanatory diagram showing the stripe domain structurewhen the applied field strength is higher than zero and less than acritical strength in the third case.

FIG. 17 is an explanatory diagram showing the stripe domain structurewhen the applied field strength is higher than or equal to the criticalstrength in the third case.

FIG. 18 is a characteristic chart showing the major loop and an initialmagnetization curve in the third case.

FIG. 19 is a characteristic chart showing an example of hysteresis loopwhen the maximum absolute value of the applied field strength is 10.2 Oein the first case.

FIG. 20 is a characteristic chart showing an example of hysteresis loopwhen the maximum absolute value of the applied field strength is 17.4 Oein the first case.

FIG. 21 is a characteristic chart showing an example of hysteresis loopwhen the maximum absolute value of the applied field strength is 21.6 Oein the first case.

FIG. 22 is a characteristic chart showing an example of hysteresis loopwhen the maximum absolute value of the applied field strength is 23.6 Oein the first case.

FIG. 23 is a characteristic chart showing an example of hysteresis loopwhen the maximum absolute value of the applied field strength is 31.6 Oein the first case.

FIG. 24 is a characteristic chart showing an example of hysteresis loopwhen the maximum absolute value of the applied field strength is 42.3 Oein the first case.

FIG. 25 is a characteristic chart showing an example of hysteresis loopwhen the maximum absolute value of the applied field strength is 10.2 Oein the second case.

FIG. 26 is a characteristic chart showing an example of hysteresis loopwhen the maximum absolute value of the applied field strength is 17.4 Oein the second case.

FIG. 27 is a characteristic chart showing an example of hysteresis loopwhen the maximum absolute value of the applied field strength is 21.6 Oein the second case.

FIG. 28 is a characteristic chart showing an example of hysteresis loopwhen the maximum absolute value of the applied field strength is 23.6 Oein the second case.

FIG. 29 is a characteristic chart showing an example of hysteresis loopwhen the maximum absolute value of the applied field strength is 31.6 Oein the second case.

FIG. 30 is a characteristic chart showing an example of hysteresis loopwhen the maximum absolute value of the applied field strength is 42.1 Oein the second case.

FIG. 31 is a characteristic chart showing an example of hysteresis loopwhen the maximum absolute value of the applied field strength is 10.3 Oein the third case.

FIG. 32 is a characteristic chart showing an example of hysteresis loopwhen the maximum absolute value of the applied field strength is 17.5 Oein the third case.

FIG. 33 is a characteristic chart showing an example of hysteresis loopwhen the maximum absolute value of the applied field strength is 21.6 Oein the third case.

FIG. 34 is a characteristic chart showing an example of hysteresis loopwhen the maximum absolute value of the applied field strength is 23.7 Oein the third case.

FIG. 35 is a characteristic chart showing an example of hysteresis loopwhen the maximum absolute value of the applied field strength is 31.6 Oein the third case.

FIG. 36 is a characteristic chart showing an example of hysteresis loopwhen the maximum absolute value of the applied field strength is 42.1 Oein the third case.

FIG. 37 is a characteristic chart showing a relationship between themaximum absolute value of the applied field strength and a magnetichysteresis parameter in the first case.

FIG. 38 is a characteristic chart showing a relationship between themaximum absolute value of the applied field strength and the magnetichysteresis parameter in the second case.

FIG. 39 is a characteristic chart showing a relationship between themaximum absolute value of the applied field strength and the magnetichysteresis parameter in the third case.

FIG. 40 is an explanatory diagram showing an example of methods fordetermining the upper limit value of the variable range of externalmagnetic field strength in the embodiment of the invention.

FIG. 41 is a characteristic chart showing a relationship between themaximum absolute value of the applied field strength and a sensitivityvariation parameter in the first case.

FIG. 42 is a characteristic chart showing experimental results on themagnetic sensor device according to the embodiment of the invention.

FIG. 43 is a characteristic chart showing experimental results on themagnetic sensor device according to the embodiment of the invention.

FIG. 44 is a characteristic chart showing experimental results on themagnetic sensor device according to the embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will now be described indetail with reference to the drawings. First, reference is made to FIG.1 to describe a schematic configuration of a magnetic sensor deviceaccording to the embodiment of the invention. The magnetic sensor device1 according to the present embodiment is a device for detectingcomponents of an external magnetic field that are in three mutuallyorthogonal directions.

The magnetic sensor device 1 includes three magnetic sensors 10, 20 and30, a soft magnetic structure 40 formed of a soft magnetic material, anda support 50. Each of the magnetic sensors 10, 20 and 30 includes atleast one magnetic detection element. The support 50 is a structuresupporting the magnetic sensors 10, 20 and 30 and the soft magneticstructure 40. The support 50 includes a substrate 51 having a topsurface 51 a and a bottom surface opposite to each other.

X, Y, and Z directions are defined here as shown in FIG. 1. The X, Y andZ directions are mutually orthogonal directions. The X and Y directionsare parallel to the top surface 51 a of the substrate 51. The Zdirection is perpendicular to the top surface 51 a of the substrate 51and directed from the bottom surface of the substrate 51 to the topsurface 51 a of the substrate 51. The opposite directions to the X, Y,and Z directions are defined as −X, −Y, and −Z directions, respectively.As used herein, the term “above” refers to positions located forward ofa reference position in the Z direction, and “below” refers to positionsopposite from the “above” positions with respect to the referenceposition. For each component of the magnetic sensor device 1, the term“top surface” refers to a surface of the component lying at the endthereof in the Z direction, and “bottom surface” refers to a surface ofthe component lying at the end thereof in the −Z direction.

The magnetic sensor 10 detects a detection-target magnetic field Hx andgenerates a detection value Sx corresponding to the detection-targetmagnetic field Hx. The detection-target magnetic field Hx has adirection parallel to a predetermined direction. In the presentembodiment, specifically, the detection-target magnetic field Hx is acomponent of an external magnetic field and is in a direction parallelto the X direction. The X direction corresponds to the first directionin the present invention. The detection-target magnetic field Hxcorresponds to the first detection-target magnetic field in the presentinvention. In the present embodiment, the strength of thedetection-target magnetic field Hx is expressed as a positive value ifthe detection-target magnetic field Hx is in the X direction, and as anegative value if the detection-target magnetic field Hx is in the −Xdirection. The detection value Sx corresponds to the first detectionvalue in the present invention.

The magnetic sensor 20 detects a detection-target magnetic field Hy andgenerates a detection value Sy corresponding to the detection-targetmagnetic field Hy. The detection-target magnetic field Hy is a componentof the external magnetic field and is in a direction parallel to the Ydirection. The Y direction corresponds to the third direction in thepresent invention. The detection-target magnetic field Hy corresponds tothe third detection-target magnetic field in the present invention. Inthe present embodiment, the strength of the detection-target magneticfield Hy is expressed as a positive value if the detection-targetmagnetic field Hy is in the Y direction, and as a negative value if thedetection-target magnetic field Hy is in the −Y direction. The detectionvalue Sy corresponds to the third detection value in the presentinvention.

The magnetic sensor 30 detects a detection-target magnetic field Hz andgenerates a detection value Sz corresponding to the detection-targetmagnetic field Hz. The detection-target magnetic field Hz is a componentof the external magnetic field and is in a direction parallel to the Zdirection. The Z direction corresponds to the second direction in thepresent invention. The detection-target magnetic field Hz corresponds tothe second detection-target magnetic field in the present invention. Inthe present embodiment, the strength of the detection-target magneticfield Hz is expressed as a positive value if the detection-targetmagnetic field Hz is in the Z direction, and as a negative value if thedetection-target magnetic field Hz is in the −Z direction. The detectionvalue Sz corresponds to the second detection value in the presentinvention.

The soft magnetic structure 40 includes a magnetic field converter 42and at least one soft magnetic layer. The magnetic field converter 42 isshown in FIGS. 5 and 6, which will be described later. The magneticfield converter 42 is configured to receive the detection-targetmagnetic field Hz and output an output magnetic field component that isin a direction perpendicular to the Z direction. The strength of theoutput magnetic field component has a correspondence with the strengthof the detection-target magnetic field Hz. The magnetic sensor 30detects the strength of the detection-target magnetic field Hz bydetecting the strength of the output magnetic field component. The softmagnetic structure 40 will be described in detail later. Note that inthe present embodiment, the “output magnetic field component”corresponds to a component of an output magnetic field vector, which isa vector representation of an output magnetic field outputted by themagnetic field converter 42, obtained by projecting the output magneticfield vector in a direction perpendicular to the Z direction. To “outputan output magnetic field component” is based on the fact that the outputmagnetic field contains an output magnetic field component which is acomponent in a direction perpendicular to the Z direction.

The magnetic sensors 10, 20 and 30 and the soft magnetic structure 40are disposed on or above the top surface 51 a of the substrate 51. Thesoft magnetic structure 40 is arranged not to overlap the magneticsensor 10 or 20 but to overlap the magnetic sensor 30 as viewed in adirection parallel to the Z direction, e.g., as viewed from above.

The support 50 has a reference plane RP parallel to the X and Ydirections. The reference plane RP is orthogonal to the Z direction. Inthe present embodiment, the reference plane RP is specifically the topsurface 51 a of the substrate 51.

The reference plane RP includes three different areas A10, A20, and A40.The area A10 is an area formed by vertically projecting the magneticsensor 10 onto the reference plane RP. The area A20 is an area formed byvertically projecting the magnetic sensor 20 onto the reference planeRP. The area A40 is an area formed by vertically projecting the softmagnetic structure 40 onto the reference plane RP. Note that an areaformed by vertically projecting the magnetic sensor 30 onto thereference plane RP coincides or substantially coincides with the areaA40.

Here, two mutually orthogonal straight lines lying in the referenceplane RP and passing through the centroid C40 of the area A40 will bereferred to as a first straight line L1 and a second straight line L2.In the present embodiment, specifically, the first straight line L1 isparallel to the X direction, and the second straight line L2 is parallelto the Y direction.

In the present embodiment, the magnetic sensor 10 includes a firstportion 11 and a second portion 12 located at different positions fromeach other. The area A10 includes a partial area A11 formed byvertically projecting the first portion 11 onto the reference plane RP,and a partial area A12 formed by vertically projecting the secondportion 12 onto the reference plane RP. The partial areas A11 and A12are located on two sides of the area A40 that are opposite to each otherin a direction parallel to the first straight line L1.

The magnetic sensor 20 includes a first portion 21 and a second portion22 located at different positions from each other. The area A20 includesa partial area A21 formed by vertically projecting the first portion 21onto the reference plane RP, and a partial area A22 formed by verticallyprojecting the second portion 22 onto the reference plane RP. Thepartial areas A21 and A22 are located on two sides of the area A40 thatare opposite to each other in a direction parallel to the secondstraight line L2.

In the present embodiment, both the partial areas A11 and A12 arelocated to be intersected by the first straight line L1. Both thepartial areas A21 and A22 are located to be intersected by the secondstraight line L2.

It is preferred that no portion of the area A10 be intersected by thesecond straight line L2. Likewise, it is preferred that no portion ofthe area A20 be intersected by the first straight line L1.

In the present embodiment, in particular, the areas A10 and A20 asviewed from above have such a positional relationship that the area A10coincides with the area A20 if the area A10 is rotated 90° around thecentroid C40 of the area A40. In FIG. 1, if the partial areas A11 andA12 are rotated 90° counterclockwise around the centroid C40, thepartial areas A11 and A12 coincide with the partial areas A21 and A22,respectively.

As shown in FIG. 1, the magnetic sensor device 1 further includes aplurality of terminals disposed on or above the top surface 51 a of thesubstrate 51. The plurality of terminals include: a power supplyterminal Vx and output terminals Vx+ and Vx− associated with themagnetic sensor 10; a power supply terminal Vy and output terminals Vy+and Vy'1 associated with the magnetic sensor 20; a power supply terminalVz and output terminals Vz+ and Vz− associated with the magnetic sensor30; and a ground terminal G shared among the magnetic sensors 10, 20 and30.

Reference is now made to FIG. 2 to describe an example circuitconfiguration of the magnetic sensor device 1. In this example, themagnetic sensor 10 includes four resistor sections Rx1, Rx2, Rx3, andRx4 constituting a Wheatstone bridge circuit. Each of the resistorsections Rx1, Rx2, Rx3 and Rx4 has a resistance that varies depending onthe detection-target magnetic field Hx. The resistor section Rx1 isprovided between the power supply terminal Vx and the output terminalVx+. The resistor section Rx2 is provided between the output terminalVx+ and the ground terminal G. The resistor section Rx3 is providedbetween the power supply terminal Vx and the output terminal Vx−. Theresistor section Rx4 is provided between the output terminal Vx− and theground terminal G.

The magnetic sensor 20 includes four resistor sections Ry1, Ry2, Ry3,and Ry4 constituting a Wheatstone bridge circuit. Each of the resistorsections Ry1, Ry2, Ry3, and Ry4 has a resistance that varies dependingon the detection-target magnetic field Hy. The resistor section Ry1 isprovided between the power supply terminal Vy and the output terminalVy+. The resistor section Ry2 is provided between the output terminalVy+ and the ground terminal G. The resistor section Ry3 is providedbetween the power supply terminal Vy and the output terminal Vy−. Theresistor section Ry4 is provided between the output terminal Vy'1 andthe ground terminal G.

The magnetic sensor 30 includes four resistor sections Rz1, Rz2, Rz3,and Rz4 constituting a Wheatstone bridge circuit. Each of the resistorsections Rz1, Rz2, Rz3, and Rz4 has a resistance that varies dependingon the output magnetic field component outputted from the magnetic fieldconverter 42. The resistor section Rz1 is provided between the powersupply terminal Vz and the output terminal Vz+. The resistor section Rz2is provided between the output terminal Vz+ and the ground terminal G.The resistor section Rz3 is provided between the power supply terminalVz and the output terminal Vz−. The resistor section Rz4 is providedbetween the output terminal Vz− and the ground terminal G.

Hereinafter, the term “resistor section R” is used to refer to any oneof the resistor sections Rx1, Rx2, Rx3, Rx4, Ry1, Ry2, Ry3, Ry4, Rz1,Rz2, Rz3, and Rz4. Each resistor section R includes at least onemagnetic detection element. In the present embodiment, the at least onemagnetic detection element is specifically at least one magnetoresistiveelement. The magnetoresistive element will hereinafter be referred to asMR element.

In the present embodiment, the MR element is specifically a spin-valveMR element. The spin-valve MR element includes a magnetization pinnedlayer which is a magnetic layer having a magnetization whose directionis fixed, a free layer which is a magnetic layer having a magnetizationwhose direction is variable depending on the direction of an appliedmagnetic field, and a gap layer located between the magnetization pinnedlayer and the free layer. The spin-valve MR element may be a tunnelingmagnetoresistive (TMR) element or a giant magnetoresistive (GMR)element. In the TMR element, the gap layer is a tunnel barrier layer. Inthe GMR element, the gap layer is a nonmagnetic conductive layer. Theresistance of the spin-valve MR element changes with the angle that themagnetization direction of the free layer forms with respect to themagnetization direction of the magnetization pinned layer. Theresistance of the spin-valve MR element is at its minimum value when theforegoing angle is 0°, and at its maximum value when the foregoing angleis 180°. In each MR element, the free layer has a shape anisotropy thatsets the direction of the magnetization easy axis to be orthogonal tothe magnetization direction of the magnetization pinned layer.

In FIG. 2, the filled arrows indicate the magnetization directions ofthe magnetization pinned layers of the MR elements. In the example shownin FIG. 2, the magnetization pinned layers of the MR elements in theresistor sections Rx1 and Rx4 have magnetizations in the X direction,and the magnetization pinned layers of the MR elements in the resistorsections Rx2 and Rx3 have magnetizations in the −X direction.

The magnetization pinned layers of the MR elements in the resistorsections Ry1 and Ry4 have magnetizations in the Y direction, and themagnetization pinned layers of the MR elements in the resistor sectionsRy2 and Ry3 have magnetizations in the −Y direction. A description willbe given later as to the magnetization directions of the magnetizationpinned layers of the MR elements in the resistor sections Rz1, Rz2, Rz3and Rz4.

A potential difference between the output terminals Vx+ and Vx− has acorrespondence with the detection-target magnetic field Hx. The magneticsensor 10 generates the detection value Sx corresponding to thepotential difference between the output terminals Vx+ and Vx−. Thedetection value Sx may be an amplitude-adjusted or offset-adjusted valueof the potential difference between the output terminals Vx+ and Vx−.The potential difference between the output terminals Vx+ and Vx− may beconverted into a numerical value representing a magnetic field strength,and the resulting value may be used as the detection value Sx.

A potential difference between the output terminals Vy+ and Vy'1 has acorrespondence with the detection-target magnetic field Hy. The magneticsensor 20 generates the detection value Sy corresponding to thepotential difference between the output terminals Vy+ and Vy−. Thedetection value Sy may be an amplitude-adjusted or offset-adjusted valueof the potential difference between the output terminals Vy+ and Vy−.The potential difference between the output terminals Vy+ and Vy'1 maybe converted into a numerical value representing a magnetic fieldstrength, and the resulting value may be used as the detection value Sy.

A potential difference between the output terminals Vz+ and Vz− has acorrespondence with the detection-target magnetic field Hz. The magneticsensor 30 generates the detection value Sz corresponding to thepotential difference between the output terminals Vz+ and Vz−. Thedetection value Sz may be an amplitude-adjusted or offset-adjusted valueof the potential difference between the output terminals Vz+ and Vz−.The potential difference between the output terminals Vz+ and Vz− may beconverted into a numerical value representing a magnetic field strength,and the resulting value may be used as the detection value Sz.

Reference is now made to FIG. 1 to describe an example layout of theresistor sections Rx1, Rx2, Rx3, Rx4, Ry1, Ry2, Ry3, and Ry4. In thisexample, the first portion 11 of the magnetic sensor 10 includes theresistor sections Rx1 and Rx4, and the second portion 12 of the magneticsensor 10 includes the resistor sections Rx2 and Rx3. The first portion21 of the magnetic sensor 20 includes the resistor sections Ry1 and Ry4,and the second portion 22 of the magnetic sensor 20 includes theresistor sections Ry2 and Ry3.

In FIG. 1, the filled arrows indicate the magnetization directions ofthe magnetization pinned layers of the MR elements. In the example shownin FIG. 1, in each of the first portion 11 of the magnetic sensor 10,the second portion 12 of the magnetic sensor 10, the first portion 21 ofthe magnetic sensor 20, and the second portion 22 of the magnetic sensor20, the magnetization pinned layers of the MR elements included thereinhave the same magnetization direction. Such an example makes it easy toset the magnetization directions of the magnetization pinned layers in aplurality of MR elements.

An example configuration of MR elements will now be described withreference to FIG. 3. An MR element 100 shown in FIG. 3 includes anantiferromagnetic layer 101, a magnetization pinned layer 102, a gaplayer 103, and a free layer 104 which are stacked in this order, fromclosest to farthest from the substrate 51. The antiferromagnetic layer101 is formed of an antiferromagnetic material, and is in exchangecoupling with the magnetization pinned layer 102 to thereby pin themagnetization direction of the magnetization pinned layer 102.

It should be appreciated that the layers 101 to 104 of the MR element100 may be stacked in the reverse order to that shown in FIG. 3. Themagnetization pinned layer 102 need not necessarily be a singleferromagnetic layer but may have an artificial antiferromagneticstructure including two ferromagnetic layers and a nonmagnetic metallayer interposed between the two ferromagnetic layers. The MR element100 may be configured without the antiferromagnetic layer 101. Themagnetic detection element may be an element for detecting a magneticfield other than the MR element, such as a Hall element or a magneticimpedance element.

Next, an example configuration of the resistor section R will bedescribed with reference to FIG. 4. In this example, the resistorsection R includes a plurality of MR elements 100 connected in series.The resistor section R further includes one or more connection layersfor electrically connecting two MR elements 100 that are adjacent toeach other in circuit configuration, so that the plurality of MRelements 100 are connected in series. In the example shown in FIG. 4 theresistor section R includes, as the one or more connection layers, oneor more lower connection layers 111 and one or more upper connectionlayers 112. The lower connection layer 111 is in contact with the bottomsurfaces of two MR elements 100 adjacent to each other in circuitconfiguration, and electrically connects the two MR elements 100. Theupper connection layer 112 is in contact with the top surfaces of two MRelements 100 adjacent to each other in circuit configuration, andelectrically connects the two MR elements 100.

Next, an example configuration of the magnetic field converter 42 of thesoft magnetic structure 40 will be described with reference to FIG. 5.In this example, the magnetic field converter 42 includes: a lower yoke42B1 and an upper yoke 42T1 associated with the resistor section Rz1; alower yoke 42B2 and an upper yoke 42T2 associated with the resistorsection Rz2; a lower yoke 42B3 and an upper yoke 42T3 associated withthe resistor section Rz3; and a lower yoke 42B4 and an upper yoke 42T4associated with the resistor section Rz4.

The lower yokes 42B1, 42B2, 42B3 and 42B4 and the upper yokes 42T1,42T2, 42T3 and 42T4 each have a rectangular parallelepiped shapeelongated in a direction perpendicular to the Z direction.

The lower yoke 42B1 and the upper yoke 42T1 are located near theresistor section Rz1. The lower yoke 42B1 is located closer to the topsurface 51 a of the substrate 51 than the resistor section Rz1. Theupper yoke 42T1 is located farther from the top surface 51 a of thesubstrate 51 than the resistor section Rz1. As viewed from above, theresistor section Rz1 lies between the lower yoke 42B1 and the upper yoke42T1.

The lower yoke 42B2 and the upper yoke 42T2 are located near theresistor section Rz2. The lower yoke 42B2 is located closer to the topsurface 51 a of the substrate 51 than is the resistor section Rz2. Theupper yoke 42T2 is located farther from the top surface 51 a of thesubstrate 51 than the resistor section Rz2. As viewed from above, theresistor section Rz2 lies between the lower yoke 42B2 and the upper yoke42T2.

The lower yoke 42B3 and the upper yoke 42T3 are located near theresistor section Rz3. The lower yoke 42B3 is located closer to the topsurface 51 a of the substrate 51 than the resistor section Rz3. Theupper yoke 42T3 is located farther from the top surface 51 a of thesubstrate 51 than the resistor section Rz3. As viewed from above, theresistor section Rz3 lies between the lower yoke 42B3 and the upper yoke42T3.

The lower yoke 42B4 and the upper yoke 42T4 are located near theresistor section Rz4. The lower yoke 42B4 is located closer to the topsurface 51 a of the substrate 51 than the resistor section Rz4. Theupper yoke 42T4 is located farther from the top surface 51 a of thesubstrate 51 than the resistor section Rz4. As viewed from above, theresistor section Rz4 lies between the lower yoke 42B4 and the upper yoke42T4.

The output magnetic field component outputted by the magnetic fieldconverter 42 contains a magnetic field component that is generated bythe lower yoke 42B1 and the upper yoke 42T1 and applied to the resistorsection Rz1, a magnetic field component that is generated by the loweryoke 42B2 and the upper yoke 42T2 and applied to the resistor sectionRz2, a magnetic field component that is generated by the lower yoke 42B3and the upper yoke 42T3 and applied to the resistor section Rz3, and amagnetic field component that is generated by the lower yoke 42B4 andthe upper yoke 42T4 and applied to the resistor section Rz4.

In FIG. 5, the four hollow arrows indicate the direction of the magneticfield components applied to the resistor sections Rz1, Rz2, Rz3 and Rz4when the detection-target magnetic field Hz is in the Z direction. Onthe other hand, in FIG. 5 the four filled arrows indicate themagnetization directions of the magnetization pinned layers 102 of theMR elements 100 of the resistor sections Rz1, Rz2, Rz3 and Rz4,respectively. The magnetization directions of the magnetization pinnedlayers 102 of the MR elements 100 of the resistor sections Rz1 and Rz4are the same as the directions of the magnetic field components that areapplied to the resistor sections Rz1 and Rz4, respectively, when thedetection-target magnetic field Hz is in the Z direction. Themagnetization directions of the magnetization pinned layers 102 of theMR elements 100 of the resistor sections Rz2 and Rz3 are opposite to thedirections of the magnetic field components that are applied to theresistor sections Rz2 and Rz3, respectively, when the detection-targetmagnetic field Hz is in the Z direction.

Now, the function of the magnetic sensor 30 will be described. Whenthere is no detection-target magnetic field Hz, the magnetizationdirection of the free layer 104 of each MR element 100 in the resistorsections Rz1, Rz2, Rz3 and Rz4 is perpendicular to the magnetizationdirection of the magnetization pinned layer 102.

If the detection-target magnetic field Hz is in the Z direction, themagnetization direction of the free layer 104 of each MR element 100 inthe resistor sections Rz1 and Rz4 tilts toward the magnetizationdirection of the magnetization pinned layer 102 from the directionperpendicular to the magnetization direction of the magnetization pinnedlayer 102. On the other hand, the magnetization direction of the freelayer 104 of each MR element 100 in the resistor sections Rz2 and Rz3tilts toward a direction opposite to the magnetization direction of themagnetization pinned layer 102 from the direction perpendicular to themagnetization direction of the magnetization pinned layer 102. As aresult, the resistor sections Rz1 and Rz4 decrease in resistance whilethe resistor sections Rz2 and Rz3 increase in resistance, compared towhen there is no detection-target magnetic field Hz.

In contrast to this, if the detection-target magnetic field Hz is in the−Z direction, the resistor sections Rz1 and Rz4 increase in resistancewhile the resistor sections Rz2 and Rz3 decrease in resistance, comparedto when there is no detection-target magnetic field Hz.

The amount of change in the resistance of each of the resistor sectionsRz1, Rz2, Rz3 and Rz4 depends on the strength of the detection-targetmagnetic field Hz.

Changes in the direction and strength of the detection-target magneticfield Hz cause the resistor sections Rz1, Rz2, Rz3 and Rz4 to change inresistance such that the resistor sections Rz1 and Rz4 increase inresistance while the second and third resistor sections Rz2 and Rz3decrease in resistance, or such that the resistor sections Rz1 and Rz4decrease in resistance while the resistor sections Rz2 and Rz3 increasein resistance. This causes a change in a potential difference betweenthe output terminals Vz+ and Vz−. It is thus possible to detect thedetection-target magnetic field Hz based on the potential difference.

Reference is now made to FIG. 6 to describe an example of configurationsof the magnetic sensors 10, 20 and 30 and the soft magnetic structure40. FIG. 6 shows a portion of each of the magnetic sensors 10, 20 and 30and the soft magnetic structure 40. In this example, the magneticsensors 10, 20 and 30 and the soft magnetic structure 40 are disposed onthe substrate 51. The substrate 51 has the top surface 51 a and thebottom surface 51 b.

The magnetic sensor 10 includes insulating layers 66A, 67A and 68A eachformed of an insulating material, in addition to the resistor sectionsRx1, Rx2, Rx3 and Rx4. The insulating layer 66A lies on the top surface51 a of the substrate 51. The resistor sections Rx1, Rx2, Rx3 and Rx4are disposed on the insulating layer 66A. FIG. 6 shows one of the MRelements 100 included in the resistor sections Rx1, Rx2, Rx3 and Rx4,and the upper and lower connection layers 112 and 111 connected to theMR element 100. The insulating layer 67A lies on the top surface 51 a ofthe substrate 51 and surrounds the resistor sections Rx1, Rx2, Rx3 andRx4. The insulating layer 68A covers the resistor sections Rx1, Rx2, Rx3and Rx4 and the insulating layer 67A.

The magnetic sensor 20 has a configuration similar to that of themagnetic sensor 10. To be more specific, the magnetic sensor 20 includesinsulating layers 66B, 67B and 68B each formed of an insulatingmaterial, in addition to the resistor sections Ry1, Ry2, Ry3 and Ry4.The insulating layer 66B lies on the top surface 51 a of the substrate51. The resistor sections Ry1, Ry2, Ry3 and Ry4 are disposed on theinsulating layer 66B. FIG. 6 shows one of the MR elements 100 includedin the resistor sections Ry1, Ry2, Ry3 and Ry4, and the upper and lowerconnection layers 112 and 111 connected to the MR element 100. Theinsulating layer 67B lies on the top surface 51 a of the substrate 51and surrounds the resistor sections Ry1, Ry2, Ry3 and Ry4. Theinsulating layer 68B covers the resistor sections Ry1, Ry2, Ry3 and Ry4and the insulating layer 67B.

The magnetic sensor 30 includes insulating layers 61, 62, 63 and 64 eachformed of an insulating material, in addition to the resistor sectionsRz1, Rz2, Rz3 and Rz4. In the example shown in FIG. 6, the soft magneticstructure 40 includes the magnetic-field converter 42 and two softmagnetic layers 41 and 43.

The magnetic field converter 42 includes the upper yokes 42T1, 42T2,42T3 and 42T4 and the lower yokes 42B1, 42B2, 42B3 and 42B4, all ofwhich are shown in FIG. 5. In FIG. 6, the reference sign 42B representsone of the lower yokes 42B1, 42B2, 42B3 and 42B4, and the reference sign42T represents a corresponding one of the upper yokes 42T1, 42T2, 42T3and 42T4.

The soft magnetic layer 41 lies on the top surface 51 a of the substrate51. The lower yokes 42B1, 42B2, 42B3 and 42B4 are disposed on the softmagnetic layer 41. The insulating layer 61 lies on the soft magneticlayer 41 and surrounds the lower yokes 42B1, 42B2, 42B3 and 42B4.

The resistor sections Rz1, Rz2, Rz3 and Rz4 are disposed on theinsulating layer 61. FIG. 6 shows one of the MR elements 100 included inthe resistor sections Rz1, Rz2, Rz3 and Rz4, and the upper and lowerconnection layers 112 and 111 connected to the MR element 100. Theinsulating layer 62 lies on the lower yokes 42B1, 42B2, 42B3 and 42B4and the insulating layer 61, and surrounds the resistor sections Rz1,Rz2, Rz3 and Rz4.

The upper yokes 42T1, 42T2, 42T3 and 42T4 are disposed on the insulatinglayer 62. The insulating layer 63 lies on the resistor sections Rz1,Rz2, Rz3 and Rz4 and the insulating layer 62, and surrounds the upperyokes 42T1, 42T2, 42T3 and 42T4.

The soft magnetic layer 43 lies on the upper yokes 42T1, 42T2, 42T3 and42T4 and the insulating layer 63. The insulating layer 64 covers thesoft magnetic layer 43.

The soft magnetic layers 41 and 43 have the function of absorbing amagnetic flux corresponding to a magnetic field other than the outputmagnetic field component outputted from the magnetic field converter 42,and thereby preventing the magnetic field from being applied to themagnetic sensor 30.

As viewed from above, the soft magnetic layers 41 and 43 extend acrossthe entire area or almost the entire area of the magnetic sensor 30.Both of an area formed by vertically projecting the soft magnetic layer41 onto the top surface 51 a of the substrate 51, i.e., the referenceplane RP, and an area formed by vertically projecting the soft magneticlayer 43 onto the reference plane RP coincide with the area A40. An areaformed by vertically projecting the magnetic sensor 30 onto thereference plane RP coincides or almost coincides with the area A40.

In the example shown in FIG. 6, all the magnetic detection elements orMR elements 100 included in the magnetic sensors 10, 20 and 30 arelocated at equal distances from the top surface 51 a of the substrate51, i.e., the reference plane RP.

The magnetic field converter 42 may include only either the lower yokes42B1, 42B2, 42B3 and 42B4 or the upper yokes 42T1, 42T2, 42T3 and 42T4.The soft magnetic structure 40 may include only either one of the softmagnetic layers 41 and 43.

In the present embodiment, the soft magnetic structure 40 is locatednear the magnetic sensors 10 and 20. The magnetic sensors 10 and 20 andthe soft magnetic structure 40 are configured so that: when an externalmagnetic field including the detection-target magnetic field Hx isapplied to the magnetic sensor 10, the external magnetic field is alsoapplied to the soft magnetic structure 40; when an external magneticfield including the detection-target magnetic field Hy is applied to themagnetic sensor 20, the external magnetic field is also applied to thesoft magnetic structure 40; and when the soft magnetic structure 40 hasa magnetization, a magnetic field based on the magnetization of the softmagnetic structure 40 is applied to the magnetic sensors 10 and 20. Atleast part of the soft magnetic structure 40 has a stripe domainstructure.

A stripe domain structure refers to a domain structure including firstand second types of domains that are both slender and are alternatelyarranged as viewed in one direction. In a magnetic film having a stripedomain structure with no magnetic field applied thereto, the spontaneousmagnetization of the first type of domains and that of the second typeof domains contain components in mutually opposite directions.

The stripe domain structure that the at least part of the soft magneticstructure 40 has will hereinafter be referred to as the stripe domainstructure of the soft magnetic structure 40. In particular, the stripedomain structure of the soft magnetic structure 40 is a domain structureincluding first and second types of domains that are both slender andare alternately arranged as viewed in a direction parallel to the Zdirection, e.g., as viewed from above. In connection with the stripedomain structure of the soft magnetic structure 40, the direction inwhich the first and second types of domains extend as viewed from abovewill be referred to as a stripe direction. When no magnetic field isapplied to the soft magnetic structure 40, the spontaneous magnetizationof the first type of domains contains a component in the stripedirection and a component in the Z direction, and the spontaneousmagnetization of the second type of domains contains a component in thestripe direction and a component in the −Z direction. In connection withthe stripe domain structure of the soft magnetic structure 40, the firsttype of domains will be referred to as first domains, the magnetizationof the first domains will be referred to as first magnetization, thesecond type of domains will be referred to as second domains, and themagnetization of the second domains will be referred to as secondmagnetization.

The soft magnetic structure 40 may include a plurality of portionshaving stripe domain structures of mutually different stripe directions.The soft magnetic structure 40 may include a portion or portions havinga stripe domain structure and a portion or portions having no stripedomain structure. In such a case, the ratio of the volume of theportion(s) having a stripe domain structure to the volume of the entiresoft magnetic structure 40 is preferably 50% or more.

Characteristics of a hysteresis loop of the soft magnetic structure 40and behavior of the stripe domain structure will now be qualitativelydescribed with reference to FIG. 7. The strength of a magnetic fieldapplied to the soft magnetic structure 40 in a direction parallel to apredetermined direction will be referred to as an applied fieldstrength. A value corresponding to a component of the magnetization ofthe soft magnetic structure 40, the component being in the directionparallel to the predetermined direction, will be referred to as amagnetization-corresponding value. In an orthogonal coordinate systemhaving two orthogonal axes for representing the applied field strengthand the magnetization-corresponding value, one of loops traced by a pathof coordinates representing the applied field strength and themagnetization-corresponding value as the applied field strength isvaried will be referred to as a major loop, the major loop being thelargest among the foregoing loops in terms of area of the regionenclosed by it.

In the present embodiment, the whole or part of the soft magneticstructure 40 is taken as the portion to be evaluated for magnetization(hereinafter referred to as the magnetization-evaluation subjectportion), and the product of a component of the volume magnetization ofthe magnetization-evaluation subject portion in a direction parallel toa predetermined direction and the volume of the magnetization-evaluationsubject portion is taken as the magnetization-corresponding value. Inparticular, in the present embodiment, the product of a component of thevolume magnetization of the magnetization-evaluation subject portion ina direction parallel to the X direction and the volume of themagnetization evaluation subject portion will be referred to as anX-direction magnetization-corresponding value Mx. The product of acomponent of the volume magnetization of the magnetization-evaluationsubject portion in a direction parallel to the Y direction and thevolume of the magnetization-evaluation subject portion will be referredto as a Y-direction magnetization-corresponding value My.

FIG. 7 shows an example of the major loop of the soft magnetic structure40. In this example, the stripe direction of the stripe domain structureof the soft magnetic structure 40 is parallel to the X direction, andthe direction of the magnetic field applied to the soft magneticstructure 40 is also parallel to the X direction. The strength of themagnetic field applied to the soft magnetic structure 40 in thedirection parallel to the X direction will be referred to as anX-direction applied field strength AHx. FIG. 7 shows an orthogonalcoordinate system having two orthogonal axes for representing theX-direction applied field strength AHx and the X-directionmagnetization-corresponding value Mx. In this orthogonal coordinatesystem, the coordinates representing the X-direction applied fieldstrength AHx and the X-direction magnetization-corresponding value Mxwill be referred to as coordinates (AHx, Mx). In FIG. 7, the horizontalaxis represents the X-direction applied field strength AHx (Oe), and thevertical axis represents the X-direction magnetization-correspondingvalue Mx (emu). In FIG. 7, the curve denoted by the symbol MALX is themajor loop. The X-direction applied field strength AHx in FIG. 7 isexpressed as a positive value if the magnetic field applied to the softmagnetic structure 40 is in the X direction, and as a negative value ifthe magnetic field applied to the soft magnetic structure 40 is in the−X direction. The X-direction magnetization-corresponding value Mx inFIG. 7 is expressed as a positive value if the magnetization of the softmagnetic structure 40 is in the X direction, and as a negative value ifthe magnetization of the soft magnetic structure 40 is in the −Xdirection. The arrows shown near the major loop MALX indicate thedirection of movement of the coordinates (AHx, Mx) on the major loopMALX.

In FIG. 7, a point A1 on the major loop MALX corresponds to a statewhere the X-direction magnetization-corresponding value Mx is saturatedat a positive value. As the X-direction applied field strength AHx isdecreased from the state of the point A1, the coordinates (AHx, Mx) onthe major loop MALX go through points A2, A3, A4, A5, and A6 in orderand reach a point A7. The point A2 corresponds to a state where theX-direction magnetization-corresponding value Mx is almost saturated ata positive value. The point A4 corresponds to a state where theX-direction applied field strength AHx is 0. The point A6 corresponds toa state where the X-direction magnetization-corresponding value Mx isalmost saturated at a negative value. The point A7 corresponds to astate where the X-direction magnetization-corresponding value Mx issaturated at a negative value.

In FIG. 7, a point B1 is the same as the point A7. As the X-directionapplied field strength AHx is increased from the state of the point B1,the coordinates (AHx, Mx) on the major loop MALX go through points B2,B3, B4, B5, and B6 in order and reach a point B7. The point B2 is thesame as the point A6. The point B3 is the same as the point A5. Thepoint B4 corresponds to a state where the X-direction applied fieldstrength AHx is 0. The point B5 is the same as the point A3. The pointB6 is the same as the point A2. The point B7 is the same as the pointA1.

In FIG. 7, reference signs A12T, A23T, A34T, A45T, A56T, and A67Trepresent schematic views of part of the stripe domain structure asviewed from above. Reference signs A12S, A23S, A34S, A45S, A56S, andA67S represent schematic views of part of the stripe domain structure asviewed in the Y direction. The schematic views A12T and A12S correspondto a state between the points A1 and A2. The schematic views A23T andA23S correspond to a state between the points A2 and A3. The schematicviews A34T and A34S correspond to a state between the points A3 and A4.The schematic views A45T and A45S correspond to a state between thepoints A4 and A5. The schematic views A56T and A56S correspond to astate between the points A5 and A6. The schematic views A67T and A67Scorrespond to a state between the points A6 and A7.

In the schematic views A12T, A23T, A34T, A45T, A56T, and A67T,rectangles containing solid-lined arrows represent the first domains,and rectangles containing broken-lined arrows represent the seconddomains. In all the schematic views, the solid-lined arrows indicate thedirection of the first magnetization, and the broken-lined arrowsindicate the direction of the second magnetization.

Between the points A1 and A2, both the first magnetization and thesecond magnetization are substantially in the X direction.

Between the points A2 and A4, the first magnetization contains acomponent in the X direction and a component in the Z direction, and thesecond magnetization contains a component in the X direction and acomponent in the −Z direction. Between the points A2 and A4, as theX-direction applied field strength AHx decreases, the component in the Xdirection of the first magnetization and the component in the Xdirection of the second magnetization decrease, whereas the component inthe Z direction of the first magnetization and the component in the −Zdirection of the second magnetization increase. Between the points A2and A4, the foregoing behavior of the first magnetization and the secondmagnetization causes the X-direction magnetization-corresponding valueMx to decrease as the X-direction applied field strength AHx decreases.At the point A4, the X-direction magnetization-corresponding value Mxhas a positive value.

Between the points A4 and A5, some of the first domains change from thestate where the first magnetization contains the component in the Xdirection and the component in the Z direction to a state where thefirst magnetization contains a component in the −X direction and thecomponent in the Z direction, or into the second domains having thesecond magnetization containing a component in the −X direction and thecomponent in the −Z direction. Between the points A4 and A5, some of thesecond domains change from the state where the second magnetizationcontains the component in the X direction and the component in the −Zdirection to a state where the second magnetization contains thecomponent in the −X direction and the component in the −Z direction, orinto the first domains having the first magnetization containing thecomponent in the −X direction and the component in the Z direction. Thenumbers of the first and the second domains to undergo theabove-described changes increase as the X-direction applied fieldstrength AHx decreases. All or almost all of the first and seconddomains at the point A4 have completed such changes at the point A5.Between the points A4 and A5, the foregoing behavior of the stripedomain structure causes the X-direction magnetization-correspondingvalue Mx to decrease as the X-direction applied field strength AHxdecreases. Between the points A4 and A5, the ratio of the amount ofchange in the X-direction magnetization-corresponding value Mx to theamount of change in the X-direction applied field strength AHx is higherin absolute value, compared to that between the points A2 and A4.

Between the points A5 and A6, the first magnetization contains thecomponent in the −X direction and the component in the Z direction,whereas the second magnetization contains the component in the −Xdirection and the component in the −Z direction. Between the points A5and A6, as the X-direction applied field strength AHx decreases, thecomponent in the −X direction of the first magnetization and thecomponent in the −X direction of the second magnetization increase,whereas the component in the Z direction of the first magnetization andthe component in the −Z direction of the second magnetization decrease.Between the points A5 and A6, the foregoing behavior of the firstmagnetization and the second magnetization causes the X-directionmagnetization-corresponding value Mx to decrease as the X-directionapplied field strength AHx decreases. Between the points A5 and A6, theratio of the amount of change in the X-directionmagnetization-corresponding value Mx to the amount of change in theX-direction applied field strength AHx is lower in absolute value,compared to that between the points A4 and A5.

Between the points A6 and A7 and between the points B1 and B2, both thefirst magnetization and the second magnetization are substantially inthe −X direction.

Between the points B2 and B4, the first magnetization contains thecomponent in the −X direction and the component in the Z direction,whereas the second magnetization contains the component in the −Xdirection and the component in the −Z direction. Between the points B2and B4, as the X-direction applied field strength AHx increases, thecomponent in the −X direction of the first magnetization and thecomponent in the −X direction of the second magnetization decrease,whereas the component in the Z direction of the first magnetization andthe component in the −Z direction of the second magnetization increase.Between the points B2 and B4, the foregoing behavior of the firstmagnetization and the second magnetization causes the X-directionmagnetization-corresponding value Mx to increase as the X-directionapplied field strength AHx increases. At the point B4, the X-directionmagnetization-corresponding value Mx has a negative value.

Between the points B4 and B5, some of the first domains change from thestate where the first magnetization contains the component in the −Xdirection and the component in the Z direction to a state where thefirst magnetization contains the component in the X direction and thecomponent in the Z direction, or into the second domains having thesecond magnetization containing the component in the X direction and thecomponent in the −Z direction. Between the points B4 and B5, some of thesecond domains change from the state where the second magnetizationcontains the component in the −X direction and the component in the −Zdirection to a state where the second magnetization contains thecomponent in the X direction and the component in the −Z direction, orinto the first domains having the first magnetization containing thecomponent in the X direction and the component in the Z direction. Thenumbers of the first and the second domains to undergo theabove-described changes increase as the X-direction applied fieldstrength AHx increases. All or almost all of the first and seconddomains at the point B4 have completed such changes at the point B5.Between the points B4 and B5, the foregoing behavior of the stripedomain structure causes the X-direction magnetization-correspondingvalue Mx to increase as the X-direction applied field strength AHxincreases. Between the points B4 and B5, the ratio of the amount ofchange in the X-direction magnetization-corresponding value Mx to theamount of change in the X-direction applied field strength AHx is higherin absolute value, compared to that between the points B2 and B4.

The value of the X-direction applied field strength AHx at which theX-direction magnetization-corresponding value Mx becomes 0 between thepoints B4 and B5 is a coercivity Hc.

Between the points B5 and B6, the first magnetization contains thecomponent in the X direction and the component in the Z direction, andthe second magnetization contains the component in the X direction andthe component in the −Z direction. Between the points B5 and B6, as theX-direction applied field strength AHx increases, the component in the Xdirection of the first magnetization and the component in the Xdirection of the second magnetization increase, whereas the component inthe Z direction of the first magnetization and the component in the −Zdirection of the second magnetization decrease. Between the points B5and B6, the foregoing behavior of the first magnetization and the secondmagnetization causes the X-direction magnetization-corresponding valueMx to increase as the X-direction applied field strength AHx increases.Between the points B5 and B6, the ratio of the amount of change in theX-direction magnetization-corresponding value Mx to the amount of changein the X-direction applied field strength AHx is lower in absolutevalue, compared to that between the points B4 and B5.

Between the points B6 and B7, both the first magnetization and thesecond magnetization are substantially in the X direction.

The description so far has dealt with changes in the X-directionmagnetization-corresponding value Mx and the behavior of the stripedomain structure in response to changes in the X-direction applied fieldstrength AHx in the case where the stripe direction of the stripe domainstructure of the soft magnetic structure 40 is parallel to the Xdirection and the direction of the magnetic field applied to the softmagnetic structure 40 is also parallel to the X direction. The foregoingdescription applies also to a case where the stripe direction isparallel to the Y direction and the direction of the magnetic fieldapplied to the soft magnetic structure 40 is also parallel to the Ydirection. Here, the strength of the magnetic field applied to the softmagnetic structure 40 in a direction parallel to the Y direction will bereferred to as a Y-direction applied field strength AHy. If the Xdirection, the −X direction, the X-direction applied field strength AHxand the X-direction magnetization-corresponding value Mx in theforegoing description are replaced with the Y direction, the −Ydirection, the Y-direction applied field strength AHy and theY-direction magnetization-corresponding value My, respectively, theresulting description applies to changes in the Y-directionmagnetization-corresponding value My and the behavior of the stripedomain structure in response to changes in the Y-direction applied fieldstrength AHy in the case where the stripe direction is parallel to the Ydirection and the direction of the magnetic field applied to the softmagnetic structure 40 is also parallel to the Y direction. A major looptraced in an orthogonal coordinate system having two orthogonal axes forrepresenting the Y-direction applied field strength AHy and theY-direction magnetization-corresponding value My will be denoted by thesymbol MALY. The coordinates representing the Y-direction applied fieldstrength AHy and the Y-direction magnetization-corresponding value My inthis orthogonal coordinate system will be referred to as coordinates(AHy, My).

In the present embodiment, the strength of the external magnetic fieldvaries within a predetermined variable range. As the strength of theexternal magnetic field varies within the variable range, the strengthsof the detection-target magnetic fields Hx, Hy, and Hz all vary within avariable range not exceeding the variable range of the strength of theexternal magnetic field. It is desirable that as the strength of theexternal magnetic field varies within the variable range, thecoordinates representing the applied field strength and themagnetization-corresponding value in the orthogonal coordinate systemhaving two orthogonal axes for representing the applied field strengthand the magnetization-corresponding value should move within a regionenclosed by the major loop.

If the external magnetic field consists only of the detection-targetmagnetic field Hx, in other words, if the direction of the externalmagnetic field is parallel to the X direction, it is desirable that inthe orthogonal coordinate system shown in FIG. 7, the coordinates (AHx,Mx) move within the region enclosed by the major loop MALX as thestrength of the external magnetic field varies within the variablerange.

If the external magnetic field consists only of the detection-targetmagnetic field Hy, in other words, if the direction of the externalmagnetic field is parallel to the Y direction, it is desirable that inthe orthogonal coordinate system having two orthogonal axes forrepresenting the Y-direction applied field strength AHy and theY-direction magnetization-corresponding value My, the coordinates (AHy,My) move within the region enclosed by the major loop MALY as thestrength of the external magnetic field varies within the variablerange.

The direction of the external magnetic field may be other than thedirections parallel to the X and Y directions. In such a case also, itis desirable that in an orthogonal coordinate system having twoorthogonal axes for representing the applied field strength and themagnetization-corresponding value, the coordinates representing theapplied field strength and the magnetization-corresponding value movewithin a region enclosed by a major loop as the strength of the externalmagnetic field varies within the variable range.

Next, a brief description will be given of a method of forming the softmagnetic structure 40 at least part of which has a stripe domainstructure. For example, NiFe is used as the material of the softmagnetic structure 40. NiFe here preferably contains 82 to 87 weight %of Ni.

The constituents of the soft magnetic structure 40, that is, the softmagnetic layers 51 and 43, the upper yokes and the lower yokes, eachpreferably have a thickness within the range of 500 nm to 10 μm.

For example, the soft magnetic structure 40 may be formed by plating.Alternating-current demagnetization may be applied to the soft magneticstructure 40. The alternating-current demagnetization is performed bysubjecting the soft magnetic structure 40 to an alternating-currentmagnetic field that alternates in direction and decreases gradually inthe absolute value of strength.

The soft magnetic structure 40 having a stripe domain structure at leastin part can be formed without alternating-current demagnetization. Insuch a case, the soft magnetic structure 40 as initially formed caninclude a plurality of portions having stripe domain structures ofmutually different stripe directions. If a magnetic field is applied tothe soft magnetic structure 40 formed, the stripe directions of thestripe domain structures can change into directions parallel to thedirection of the applied magnetic field. The ratio of the area ofdomains including a component magnetized in the direction of the appliedmagnetic field to that of domains including a component magnetized inthe direction opposite to the direction of the applied magnetic field asviewed from above depends on the strength of the applied magnetic field.

By applying alternating-current demagnetization to the soft magneticstructure 40, it is possible to align the stripe directions of thestripe domain structures in most part of the soft magnetic structure 40.The alternating-current demagnetization also allows most part of thesoft magnetic structure 40 to be the same in ratio between the area ofdomains including a component magnetized in a predetermined directionand the area of domains including a component magnetized in a directionopposite to the predetermined direction as viewed from above.

If, for example, alternating-current demagnetization is performed byusing an alternating-current magnetic field whose direction alternatesbetween the X and −X directions, the stripe direction of the stripedomain structure becomes parallel to the X direction. Suchalternating-current demagnetization will hereinafter be referred to asX-direction alternating-current demagnetization. On the other hand, ifalternating-current demagnetization is performed by using analternating-current magnetic field whose direction alternates betweenthe Y and −Y directions, the stripe direction of the stripe domainstructure becomes parallel to the Y direction. Such alternating-currentdemagnetization will hereinafter be referred to as Y-directionalternating-current demagnetization. The stripe domain structureimmediately after alternating-current demagnetization will be referredto as an initial stripe domain structure.

In the present embodiment, the path traced by the coordinatesrepresenting the applied field strength and themagnetization-corresponding value as the applied field strength to thesoft magnetic structure 40 after alternating-current demagnetization isvaried from 0 will be referred to as an initial magnetization curve.According to the present embodiment, in the orthogonal coordinate systemhaving two orthogonal axes for representing the applied magnetic fieldstrength and the corresponding magnetization value, the coordinatesrepresenting the applied field strength and themagnetization-corresponding value move along, for example, a minor loopthat is formed within the region enclosed by the major loop and not incontact with the major loop as the strength of the external magneticfield varies within the variable range. The minor loop may start at apoint on the initial magnetization curve.

When the external magnetic field consists only of the detection-targetmagnetic field Hx, as the strength of the external magnetic field varieswithin the variable range, the coordinates (AHx, Mx) in the orthogonalcoordinate system shown in FIG. 7 move along, for example, a minor loopthat is formed within the region enclosed by the major loop MALX and notin contact with the major loop MALX. This minor loop may start at apoint on the initial magnetization curve. On the other hand, when theexternal magnetic field consists only of the detection-target magneticfield Hy, as the strength of the external magnetic field varies withinthe variable range, the coordinates (AHy, My) in the orthogonalcoordinate system having two orthogonal axes for representing theY-direction applied field strength AHy and the Y-directionmagnetization-corresponding value My move along, for example, a minorloop that is formed within the region enclosed by the major loop MALY inthis orthogonal coordinate system and not in contact with the major loopMALY. This minor loop may start at a point on the initial magnetizationcurve.

The major loops MALX and MALY have almost the same shape regardless ofthe stripe direction of the initial stripe domain structure. The reasonis as follows. In measuring the major loop MALX or MALY, a magneticfield having such a strength as to saturate the magnetization of thesoft magnetic structure 40 is applied to the soft magnetic structure 40in a predetermined direction. This makes the stripe direction of thestripe domain structure of the soft magnetic structure 40 parallel tothe foregoing predetermined direction regardless of the stripe directionof the initial stripe domain structure. The predetermined direction is adirection parallel to the X direction or a direction to the Y direction.Even if the magnetic field in the direction parallel to thepredetermined direction is subsequently changed in strength, the stripedirection remains unchanged. The same applies regardless of whether thepredetermined direction is a direction parallel to the X direction or adirection parallel to the Y direction. The major loops MALX and MALYthus have almost the same shape.

The stripe domain structure of the soft magnetic structure 40 can varydepending on the direction and strength of the magnetic field applied tothe soft magnetic structure 40 after alternating-currentdemagnetization. This will be described in detail below. A first, asecond, a third and a fourth case will be described here.

The first case is a case where a magnetic field in a direction parallelto the X direction is applied to the soft magnetic structure 40 formedby alternating-current demagnetization in the X direction. The secondcase is a case where a magnetic field in a direction parallel to the Ydirection is applied to the soft magnetic structure 40 formed byalternating-current demagnetization in the Y direction. The third caseis a case where a magnetic field in a direction parallel to the Xdirection is applied to the soft magnetic structure 40 formed byalternating-current demagnetization in the Y direction. The fourth caseis a case where a magnetic field in a direction parallel to the Ydirection is applied to the soft magnetic structure 40 formed byalternating-current demagnetization in the X direction.

To begin with, examples of respective specific methods foralternating-current demagnetization in the X direction and the Ydirection will be described. In an example of a specific method foralternating-current demagnetization in the X direction, analternating-current magnetic field whose direction alternates betweenthe X direction and the −X direction and whose strength decreasesgradually in absolute value is applied to the soft magnetic structure40. The alternating-current magnetic field is a magnetic field whosestrength decreases to 80% in absolute value each time the direction isswitched. The initial direction of the alternating-current magneticfield is the X direction, and the absolute value of strength is 100 Oe.An example of a specific method for alternating-current demagnetizationin the Y direction is the same as the example of the specific method foralternating-current demagnetization in the X direction except that the Xand −X directions are replaced with the Y and −Y directions,respectively.

The first case will now be described. In the first case, although notshown in the drawings, the stripe direction of the initial stripe domainstructure is parallel to the X direction. The direction of amagnetization component parallel to the XY plane in each domain iseither the X direction or the −X direction. The magnetization componentparallel to the XY plane will hereinafter be referred to as an in-planemagnetization component. A magnetization component perpendicular to theXY plane will be referred to as a perpendicular magnetization component.

In the initial stripe domain structure in the first case, the first andsecond domains are alternately arranged in the Y direction. A bundle ofa plurality of domains in which the in-plane magnetization componentsare in the same direction will be referred to as a domain bundle. Theinitial stripe domain structure in the first case includes first domainbundles and second domain bundles alternately arranged in the Ydirection. The first domain bundle is a bundle of a plurality of domainsin which the in-plane magnetization components are in the X direction.The second domain bundle is a bundle of a plurality of domains in whichthe in-plane magnetization components are in the −X direction. In theinitial stripe domain structure in the first case, magnetic wallsextending in the X direction are formed between every adjacent first andsecond domain bundles.

In the first case, the stripe direction of the stripe domain structureremains unchanged even if a magnetic field in a direction parallel tothe X direction is applied to the soft magnetic structure 40 formed byalternating-current demagnetization in the X direction. When theX-direction applied field strength AHx is changed, the stripe domainstructure exhibits the same behavior as that described with reference toFIG. 7.

Next, the major and minor loops in the first case will be described.FIG. 8 is a characteristic chart showing an example of the major andminor loops in the first case. FIG. 9 is a characteristic chart showinga portion of FIG. 8 on an enlarged scale. In FIGS. 8 and 9, thehorizontal axis represents the X-direction applied field strength AHx(Oe), and the vertical axis represents the X-directionmagnetization-corresponding value Mx (emu).

Here, a measurement method for the major and minor loops employed in thepresent embodiment will be described briefly. The measurement methoduses a sample composed of a plurality of elements arranged such that anumber of the plurality of elements align in each of the X and Ydirections. As viewed from above, each element has a square shape with aside of approximately 260 μm in length. Each element has a thickness ofapproximately 2 μm. In the sample, the spacing between every twoadjacent elements is set at 100 μm or more to thereby prevent magneticcoupling between adjacent elements. As viewed from above, the entiresample has a square shape with a side of approximately 10 mm in length.The magnetic field applied to the sample is generated by using aHelmholtz coil. The magnetization-corresponding value of the sample ismeasured by using a vibrating sample magnetometer.

In FIGS. 8 and 9, the curve denoted by the symbol MALX is the major loopMALX. The major loop MALX is a path traced by the coordinates (AHx, Hx)when the X-direction applied field strength AHx is set to 250 Oe, thengradually reduced to −250 Oe, and then gradually increased to 250 Oe.

In FIGS. 8 and 9, the hysteresis loop denoted by the reference numeral73 is an example of the minor loop. This hysteresis loop 73 is a pathtraced by the coordinates (AHx, Mx) when the X-direction applied fieldstrength AHx is set to 21.6 Oe, then gradually reduced to −21.6 Oe, andthen gradually increased to 21.6 Oe. The hysteresis loop 73 is a minorloop that is formed within the region enclosed by the major loop MALXand not in contact with the major loop MALX. This minor loop starts at apoint on the initial magnetization curve.

Next, the second case will be described. In the second case, althoughnot shown in the drawings, the stripe direction of the initial stripedomain structure is parallel to the Y direction. The direction of thein-plane magnetization component in each domain is either the Ydirection or the −Y direction.

In the initial stripe domain structure in the second case, the first andsecond domains are alternately arranged in the X direction. The initialstripe domain structure in the second case includes third domain bundlesand fourth domain bundles alternately arranged in the X direction. Thethird domain bundle is a bundle of a plurality of domains in which thein-plane magnetization components are in the Y direction. The fourthdomain bundle is a bundle of a plurality of domains in which thein-plane magnetization components are in the −Y direction. In theinitial stripe domain structure in the second case, magnetic wallsextending in the Y direction are formed between every adjacent third andfourth domain bundles.

In the second case, the stripe direction of the stripe domain structureremains unchanged even if a magnetic field in a direction parallel tothe Y direction is applied to the soft magnetic structure 40 formed byalternating-current demagnetization in the Y direction. When theY-direction applied field strength AHy is changed, the stripe domainstructure exhibits the same behavior as that exhibited by the stripedomain structure when the X-direction applied field strength AHx ischanged.

Next, the major and minor loops in the second case will be described.FIG. 10 is a characteristic chart showing an example of the major andminor loops in the second case. FIG. 11 is a characteristic chartshowing a portion of FIG. 10 on an enlarged scale. In FIGS. 10 and 11,the horizontal axis represents the Y-direction applied field strengthAHy (Oe), and the vertical axis represents the Y-directionmagnetization-corresponding value My (emu). The Y-direction appliedfield strength AHy in FIGS. 10 and 11 is expressed as a positive valueif the magnetic field applied to the soft magnetic structure 40 is inthe Y direction, and as a negative value if the magnetic field appliedto the soft magnetic structure 40 is in the −Y direction. TheY-direction magnetization-corresponding value My in FIGS. 10 and 11 isexpressed as a positive value if the magnetization of the soft magneticstructure 40 is in the Y direction, and as a negative value if themagnetization of the soft magnetic structure 40 is in the −Y direction.

In FIGS. 10 and 11, the curve denoted by the symbol MALY is the majorloop MALY. The major loop MALY is a path traced by the coordinates (AHy,My) when the Y-direction applied field strength AHy is set to 250 Oe,then gradually reduced to −250 Oe, and then gradually increased to 250Oe.

In FIGS. 10 and 11, the hysteresis loop denoted by the reference numeral83 is an example of the minor loop. The hysteresis loop 83 is a pathtraced by the coordinates (AHy, My) when the Y-direction applied fieldstrength AHy is set to 21.6 Oe, then gradually reduced to −21.6 Oe, andthen gradually increased to 21.6 Oe. The hysteresis loop 83 is a minorloop that is formed within the region enclosed by the major loop MALYand not in contact with the major loop MALY. The minor loop starts at apoint on the initial magnetization curve.

Next, the third case will be described. Although not shown in thedrawings, the initial stripe domain structure in the third case is thesame as the initial stripe domain structure in the second case. Thestripe direction of the initial stripe domain structure is parallel tothe Y direction. The initial stripe domain structure in the third casewill be described in detail later.

In the third case, if a magnetic field in a direction parallel to the Xdirection is applied to the soft magnetic structure 40 formed byalternating-current demagnetization in the Y direction and theX-direction applied field strength AHx is increased from 0, the stripedirection of the stripe domain structure rotates from the directionparallel to the Y direction to the direction parallel to the X directionwhen the X-direction applied field strength AHx reaches or exceeds acertain strength. The strength of the magnetic field at which such arotation of the stripe direction occurs will be referred to as acritical strength.

A detailed description will be given later as to the behavior of thestripe domain structure when the magnetic field in the directionparallel to the X direction is applied to the soft magnetic structure 40in the third case.

Next, the major and minor loops in the third case will be described.FIG. 12 is a characteristic chart showing an example of the major andminor loops in the third case. FIG. 13 is a characteristic chart showinga portion of FIG. 12 on an enlarged scale. In FIGS. 12 and 13, thehorizontal axis represents the X-direction applied field strength AHx(Oe), and the vertical axis represents the X-directionmagnetization-corresponding value Mx (emu).

In FIGS. 12 and 13, the curve denoted by the symbol MALX is the majorloop MALX. The major loop MALX is a path traced by the coordinates (AHx,Hx) when the X-direction applied field strength AHx is set to 250 Oe,then gradually reduced to −250 Oe, and then gradually increased to 250Oe.

In FIGS. 12 and 13, the hysteresis loop denoted by the reference numeral93 is an example of the minor loop. This hysteresis loop 93 is a pathtraced by the coordinates (AHx, Mx) when the X-direction applied fieldstrength AHx is set to 21.6 Oe, then gradually reduced to −21.6 Oe, andthen gradually increased to 21.6 Oe. The hysteresis loop 93 is a minorloop that is formed within the region enclosed by the major loop MALXand not in contact with the major loop MALX. This minor loop starts at apoint on the initial magnetization curve.

Next, the initial stripe domain structure in the third case will bedescribed with reference to FIG. 14. FIG. 14 shows the initial stripedomain structure in the third case. FIG. 14 schematically illustratesthe first and second domains by white and black gradations. In FIG. 14,regions closer to white than an intermediate gradation value correspondto the first domains, and regions closer to black than the intermediategradation value correspond to the second domains.

A single domain includes a plurality of magnetic dipoles having a spinmagnetic moment in substantially the same direction. A component of thespin magnetic moment parallel to the XY plane will be referred to as anin-plane spin component. A component of the spin magnetic momentperpendicular to the XY plane will be referred to as a perpendicularspin component. In a domain, the direction of the in-plane magnetizationcomponent is the same as that of in-plane spin components of theplurality of magnetic dipoles in the domain. The direction of theperpendicular magnetization component is the same as that of theperpendicular spin components of the plurality of magnetic dipoles inthe domain.

FIG. 14 schematically illustrates the directions and magnitudes of theperpendicular spin components in the domains by black and whitegradations. In FIG. 14, regions closer to white than the intermediategradation value indicate that the perpendicular spin components are inthe Z direction, and that the closer to white, the greater theperpendicular spin components. Regions closer to black than theintermediate gradation value indicate that the perpendicular spincomponents are in the −Z direction, and that the closer to black, thegreater the perpendicular spin components.

FIG. 14 also shows the directions of the in-plane and perpendicular spincomponents of the magnetic dipoles by arrows. In FIG. 14, the directionsof the arrows indicate the directions of the in-plane spin components.Black arrows indicate that the perpendicular spin components are in theZ direction. White arrows indicate that the perpendicular spincomponents are in the −Z direction.

As shown in FIG. 14, in the third case, the stripe direction of theinitial stripe domain structure is parallel to the Y direction. Thedirection of the in-plane magnetization component in each domain and thedirection of the in-plane spin component of each magnetic dipole areeither the Y direction or the −Y direction. In the initial stripe domainstructure in the third case, the first and second domains arealternately arranged in the X direction. In the initial stripe domainstructure in the third case, the third and fourth domain bundlesdescribed in relation to the second case are formed to be alternatelyarranged in the X direction. The third domain bundles will hereinafterbe denoted by the reference numeral 203, and the fourth domain bundlesby the reference numeral 204. Magnetic walls W extending in the Ydirection are formed between every adjacent third and fourth domainbundles 203 and 204. The directions of the spin magnetic moments changegreatly inside the magnetic walls W.

In similar diagrams to FIG. 14 to be referred to for descriptions below,the first domains, second domains, spin magnetic moments and magneticwalls are illustrated in the same manner as in FIG. 14.

In the initial stripe domain structure in the third case, the number ofmagnetic dipoles having an in-plane spin component in the Y direction isalmost the same as that of magnetic dipoles having an in-plane spincomponent in the −Y direction. In the initial stripe domain structure inthe third case, the number of magnetic dipoles having a perpendicularspin component in the Z direction is almost the same as that of magneticdipoles having a perpendicular spin component in the −Z direction. Theinitial stripe domain structure in the third case includes no or fewmagnetic dipoles having an in-plane spin component in the X or −Xdirection. Consequently, the magnetization component of the entire softmagnetic structure 40 parallel to the X direction is zero or almostzero.

Next, with reference to FIGS. 15 to 17, a description will be given ofthe behavior of the stripe domain structure when a magnetic field in adirection parallel to the X direction is applied to the soft magneticstructure 40 in the third case. By way of example, the followingdescription deals with a case where a magnetic field in the X directionis applied to the soft magnetic structure 40 and the X-direction appliedfield strength AHx is increased from 0.

FIG. 15 shows the stripe domain structure when the X-direction appliedfield strength AHx is 0. While FIG. 15 shows a portion of FIG. 14 on anenlarged scale, the stripe domain structure shown in FIG. 15 is the sameas the initial stripe domain structure shown in FIG. 14.

As the X-direction applied field strength AHx is increased from 0, thedirections of the in-plane spin components tilt from the Y and −Ydirections toward the X direction. The tilt amounts of the directions ofthe in-plane spin components increase as the X-direction applied fieldstrength AHx increases. If the X-direction applied field strength AHxreaches or exceeds the critical strength, the magnetic walls W move toreduce magnetostatic energy. The magnetic dipoles are quickly rearrangedaccordingly, and the stripe direction rotates from the directionparallel to the Y direction to the direction parallel to the Xdirection.

FIG. 16 shows the stripe domain structure when the X-direction appliedfield strength AHx is greater than 0 and less than the criticalstrength. In FIG. 16 and other similar diagrams, the length of the arrowdenoted by AHx schematically indicates the X-direction applied fieldstrength AHx. As shown in FIG. 16, if the X-direction applied fieldstrength AHx is greater than 0 and less than the critical strength, thedirections of the in-plane spin components tilt from the Y and −Ydirections toward the X direction. In the state shown in FIG. 16, themagnetic wall W has not yet moved, and the stripe direction remainsparallel to the Y direction.

FIG. 17 shows the stripe domain structure when the X-direction appliedfield strength AHx is greater than or equal to the critical strength. Asshown in FIG. 17, if the X-direction applied field strength AHx reachesor exceeds the critical strength, the magnetic wall W moves. Thein-plane spin components become oriented in the X direction, and thestripe direction becomes parallel to the X direction. In the state shownin FIG. 17, the first and second domains are alternately arranged in theY direction. All the in-plane magnetization components are in the Xdirection.

If the X-direction applied field strength AHx is then increased untilthe X-direction magnetization-corresponding value Mx of the softmagnetic structure 40 is saturated, the spin magnetic moments becomeoriented in the X direction or substantially in the X direction.

FIG. 18 is a characteristic chart showing the major loop and the initialmagnetization curve in the third case. In FIG. 18, the horizontal axisrepresents the X-direction applied field strength AHx (Oe), and thevertical axis represents the X-direction magnetization-correspondingvalue Mx (emu). In FIG. 18, the curve denoted by the symbol MALX is themajor loop, and the curve denoted by the symbol MCi is the initialmagnetization curve. The major loop MALX shown in FIG. 18 is the same asthe major loop MALX shown in FIG. 12.

In FIG. 18, a point C1 on the initial magnetization curve MCicorresponds to a state where the X-direction applied field strength AHxis 0 after alternating-current demagnetization in the Y direction. Apoint C2 on the initial magnetization curve MCi corresponds to a statewhere the X-direction applied field strength AHx is greater than 0 andless than the critical strength. A point C3 on the initial magnetizationcurve MCi corresponds to a state where the X-direction applied fieldstrength AHx is greater than or equal to the critical strength. A pointC4 on the initial magnetization curve MCi corresponds to a state wherethe X-direction applied field strength AHx is sufficiently greater thanthe critical strength. The initial magnetization curve MCi joins themajor loop MALX if the stripe direction becomes parallel to the Xdirection.

In the range of the X-direction applied field strength AHx correspondingto the range of the initial magnetization curve MCi between the pointsC2 and C4 (the points C2 and C4 excluded), the X-directionmagnetization-corresponding value Mx on the initial magnetization curveMCi is smaller than that on the major loop MALX for the same X-directionapplied field strength AHx. The reason is that, in such a range, thestripe direction is not fully parallel to the X direction. In theforegoing range, the initial magnetization curve MCi protrudes from themajor loop MALX.

Next, the fourth case will be described. Although not shown in thedrawings, the initial stripe domain structure in the fourth case is thesame as the initial stripe domain structure in the first case. Thestripe direction of the initial stripe domain structure is parallel tothe X direction. In the fourth case, a magnetic field in a directionparallel to the Y direction is applied to the soft magnetic structure 40formed by alternating-current demagnetization in the X direction, andthe Y-direction applied field strength AHy is increased from 0. When theY-direction applied field strength AHy reaches or exceeds the criticalstrength, the stripe direction of the stripe domain structure rotatesfrom the direction parallel to the X direction to the direction parallelto the Y direction.

Next, a description will be given of the results of a first experiment,which studied the magnetic hysteresis characteristic of the softmagnetic structure 40 in the first and third cases. To enable aquantitative evaluation of the magnetic hysteresis characteristic of thesoft magnetic structure 40, magnetic hysteresis parameters of the softmagnetic structure 40 are defined as described below. Different magnetichysteresis parameters are defined for cases where the direction of themagnetic field applied to the soft magnetic structure 40 is parallel tothe X direction and where the direction of the magnetic field applied tothe soft magnetic structure 40 is parallel to the Y direction. Themagnetic hysteresis parameter in the case where the direction of themagnetic field applied to the soft magnetic structure 40 is parallel tothe X direction will be referred to as an X-direction magnetichysteresis parameter HPHx. The magnetic hysteresis parameter in the casewhere the direction of the magnetic field applied to the soft magneticstructure 40 is parallel to the Y direction will be referred to as aY-direction magnetic hysteresis parameter HPHy.

The X-direction magnetic hysteresis parameter HPHx is determined fromthe X-direction magnetization-corresponding value Mx obtained with theX-direction applied field strength AHx to the soft magnetic structure 40varied after alternating-current demagnetization. In the presentembodiment, the X-direction magnetic hysteresis parameter HPHx is avalue determined as follows. The X-direction applied field strength AHxis set to a predetermined value MHx greater than 0, then decreased to−MHx, and then increased to the predetermined value MHx. The X-directionmagnetization-corresponding value Mx at which the X-direction appliedfield strength AHx reaches 0 in the process of increasing is subtractedfrom the X-direction magnetization-corresponding value Mx at which theX-direction applied field strength AHx reaches 0 in the process ofdecreasing. The resulting value is the X-direction magnetic hysteresisparameter HPHx.

Similarly, the Y-direction magnetic hysteresis parameter HPHy isdetermined from the Y-direction magnetization-corresponding value Myobtained with the Y-direction applied field strength AHy to the softmagnetic structure 40 varied after alternating-current demagnetization.In the present embodiment, the Y-direction magnetic hysteresis parameterHPHy is a value determined as follows. The Y-direction applied fieldstrength AHy is set to a predetermined value MHy greater than 0, thendecreased to −MHy, and then increased to the predetermined value MHy.The Y-direction magnetization-corresponding value My at which theY-direction applied field strength AHx reaches 0 in the process ofincreasing is subtracted from the Y-directionmagnetization-corresponding value My at which the Y-direction appliedfield strength AHy reaches 0 in the process of decreasing. The resultingvalue is the Y-direction magnetic hysteresis parameter HPHy.

To enable a quantitative evaluation of the hysteresis characteristics ofthe detection values of the magnetic sensors 10 and 20, the respectivehysteresis parameters of the magnetic sensors 10 and 20 are defined asdescribed below. The hysteresis parameter of the magnetic sensor 10 isdetermined from the detection value Sx obtained with the strength of thedetection-target magnetic field Hx varied after subjecting the softmagnetic structure 40 to alternating-current demagnetization.Specifically, the hysteresis parameter of the magnetic sensor 10 is avalue determined as follows. The strength of the detection-targetmagnetic field Hx is set to a predetermined value Px greater than 0,then decreased to −Px, and then increased to 0. The detection value Sxat which the strength of the detection-target magnetic field Hx reaches0 in the process of increasing is subtracted from the detection value Sxat which the strength of the detection-target magnetic field Hx reaches0 in the process of decreasing. The resulting value is the hysteresisparameter of the magnetic sensor 10.

Similarly, the hysteresis parameter of the magnetic sensor 20 isdetermined from the detection value Sy obtained with the strength of thedetection-target magnetic field Hy varied after subjecting the softmagnetic structure 40 to alternating-current demagnetization.Specifically, the hysteresis parameter of the magnetic sensor 20 is avalue determined as follows. The strength of the detection-targetmagnetic field Hy is set to a predetermined value Py greater than 0,then decreased to −Py, and then increased to 0. The detection value Syat which the strength of the detection-target magnetic field Hy reaches0 in the process of increasing is subtracted from the detection value Syat which the strength of the detection-target magnetic field Hx reaches0 in the process of decreasing. The resulting value is the hysteresisparameter of the magnetic sensor 20.

The greater the value of the X-direction magnetic hysteresis parameterHPHx, the greater the value of the hysteresis parameter of the magneticsensor 10. The greater the value of the hysteresis parameter of themagnetic sensor 10, the more the detection accuracy of the magneticsensor 10 can be said to drop. Similarly, the greater the value of theY-direction magnetic hysteresis parameter HPHy, the greater the value ofthe hysteresis parameter of the magnetic sensor 20. The greater thevalue of the hysteresis parameter of the magnetic sensor 20, the morethe detection accuracy of the magnetic sensor 20 can be said to drop. Tominimize a drop in the detection accuracy of the magnetic sensors 10 and20 due to the magnetic hysteresis characteristic of the soft magneticstructure 40, the smaller the better the values of the X- andY-direction magnetic hysteresis parameters HPHx and HPHy.

In the experiment on each of the first and third cases, a hysteresisloop starting at a point on the initial magnetization curve obtainedwith varying X-direction applied field strength AHx was measured, andthe X-direction magnetic hysteresis parameter HPHx was determined fromthe hysteresis loop. In the experiment, the value of MHx at which theabsolute value of the X-direction applied field strength AHx wasmaximized in measuring the hysteresis loop was varied to measurerespective hysteresis loops for different MHx values, and therelationship between MHx and the magnetic hysteresis parameter HPHx wasdetermined.

In the experiment on the second case, a hysteresis loop starting at apoint on the initial magnetization curve obtained with varyingY-direction applied field strength AHy was measured, and the Y-directionmagnetic hysteresis parameter HPHy was determined from the hysteresisloop. In the experiment, the value of MHy at which the absolute value ofthe Y-direction applied field strength AHy was maximized in measuringthe hysteresis loop was varied to measure respective hysteresis loopsfor different MHy values, and the relationship between MHy and themagnetic hysteresis parameter HPHy was determined.

FIGS. 19 to 24 are characteristic charts showing examples of thehysteresis loops in the first case. In FIGS. 19 to 24, the horizontalaxis represents the X-direction applied field strength AHx (Oe), and thevertical axis represents the X-direction magnetization-correspondingvalue Mx (emu). In FIGS. 19 to 24, the curve denoted by the symbol MALXis the major loop MALX. The major loop MALX is the same as that shown inFIGS. 8 and 9.

FIG. 19 shows an example of the hysteresis loop for an MHx of 10.2 Oe,denoted by the reference numeral 71. FIG. 20 shows an example of thehysteresis loop for an MHx of 17.4 Oe, denoted by the reference numeral72. FIG. 21 shows an example of the hysteresis loop for an MHx of 21.6Oe, denoted by the reference numeral 73. The hysteresis loop 73 is thesame as the hysteresis loop 73 shown in FIGS. 8 and 9. FIG. 22 shows anexample of the hysteresis loop for an MHx of 23.6 Oe, denoted by thereference numeral 74. FIG. 23 shows an example of the hysteresis loopfor an MHx of 31.6 Oe, denoted by the reference numeral 75. FIG. 24shows an example of the hysteresis loop for an MHx of 42.3 Oe, denotedby the reference numeral 76.

FIGS. 25 to 30 are characteristic charts showing examples of thehysteresis loops in the second case. In FIGS. 25 to 30, the horizontalaxis represents the Y-direction applied field strength AHy (Oe), and thevertical axis represents the Y-direction magnetization-correspondingvalue My (emu). In FIGS. 25 to 30, the curve denoted by the symbol MALYis the major loop MALY. The major loop MALY is the same as that shown inFIGS. 10 and 11.

FIG. 25 shows an example of the hysteresis loop for an MHy of 10.2 Oe,denoted by the reference numeral 81. FIG. 26 shows an example of thehysteresis loop for an MHy of 17.4 Oe, denoted by the reference numeral82. FIG. 27 shows an example of the hysteresis loop for an MHy of 21.6Oe, denoted by the reference numeral 83. The hysteresis loop 83 is thesame as the hysteresis loop 83 shown in FIGS. 10 and 11. FIG. 28 showsan example of the hysteresis loop for an MHy of 23.6 Oe, denoted by thereference numeral 84. FIG. 29 shows an example of the hysteresis loopfor an MHy of 31.6 Oe, denoted by the reference numeral 85. FIG. 30shows an example of the hysteresis loop for an MHy of 42.1 Oe, denotedby the reference numeral 86.

FIGS. 31 to 36 are characteristic charts showing examples of thehysteresis loops in the third case. In FIGS. 31 to 36, the horizontalaxis represents the X-direction applied field strength AHx (Oe), and thevertical axis represents the X-direction magnetization-correspondingvalue Mx (emu). In FIGS. 31 to 36, the curve denoted by the symbol MALXis the major loop MALX. The major loop MALX is the same as that shown inFIGS. 12 and 13.

FIG. 31 shows an example of the hysteresis loop for an MHx of 10.3 Oe,denoted by the reference numeral 91. FIG. 32 shows an example of thehysteresis loop for an MHx of 17.5 Oe, denoted by the reference numeral92. FIG. 33 shows an example of the hysteresis loop for an MHx of 21.6Oe, denoted by the reference numeral 93. The hysteresis loop 93 is thesame as the hysteresis loop 93 shown in FIGS. 12 and 13. FIG. 34 showsan example of the hysteresis loop for an MHx of 23.7 Oe, denoted by thereference numeral 94. FIG. 35 shows an example of the hysteresis loopfor an MHx of 31.6 Oe, denoted by the reference numeral 95. FIG. 36shows an example of the hysteresis loop for an MHx of 42.1 Oe, denotedby the reference numeral 96.

FIG. 37 is a characteristic chart showing a relationship between MHx andthe magnetic hysteresis parameter HPHx in the first case. In FIG. 37,the horizontal axis represents MHx (Oe), and the vertical axisrepresents the magnetic hysteresis parameter HPHx (emu). In FIG. 37, thebroken line denoted by the reference numeral 77 indicates a positionwhere MHx is 17.4 Oe. The broken line denoted by the reference numeral78 indicates a position where MHx is 21.6 Oe.

FIG. 38 is a characteristic chart showing a relationship between MHy andthe magnetic hysteresis parameter HPHy in the second case. In FIG. 38,the horizontal axis represents MHy (Oe), and the vertical axisrepresents the magnetic hysteresis parameter HPHy (emu). In FIG. 38, thebroken line denoted by the reference numeral 87 indicates a positionwhere MHy is 17.4 Oe. The broken line denoted by the reference numeral88 indicates a position where MHy is 21.6 Oe.

FIG. 39 is a characteristic chart showing a relationship between MHx andthe magnetic hysteresis parameter HPHx in the third case. In FIG. 39,the horizontal axis represents MHx (Oe), and the vertical axisrepresents the magnetic hysteresis parameter HPHx (emu). In FIG. 39, thebroken line denoted by the reference numeral 97 indicates a positionwhere MHx is 21.6 Oe.

Each of MHx and MHy will hereinafter be referred to as an upper limitvalue of the applied field strength. As shown in FIGS. 37 to 39, in allof the first to third cases the value of the magnetic hysteresisparameter tends to increase as the upper limit value of the appliedfield strength increases. In all of the first to third cases, thegradient of change in the value of the magnetic hysteresis parameterwith respect to a change in the upper limit value of the applied fieldstrength becomes large if the upper limit value of the applied fieldstrength exceeds 21.6 Oe. In the third case, as shown in FIGS. 31 to 33,the hysteresis loop starting at a point on the initial magnetizationcurve is not in contact with the major loop MALX until the upper limitvalue of the applied field strength reaches 21.6 Oe. As shown in FIGS.34 to 36, if the upper limit value of the applied field strength exceeds21.6 Oe, the hysteresis loop starting at a point on the initialmagnetization curve protrudes from the major loop MALX. Although notshown in the drawings, in the fourth case, the hysteresis loop startingat a point on the initial magnetization curve is not in contact with themajor loop MALY, either, until the upper limit value of the appliedfield strength reaches 21.6 Oe. If the upper limit value of the appliedfield strength exceeds 21.6 Oe, the hysteresis loop starting at a pointon the initial magnetization curve protrudes from the major loop MALY.In each of the first and second cases, the hysteresis loop starting at apoint on the initial magnetization curve is not in contact with themajor loop, either, until the upper limit value of the applied magneticfield strength reaches 21.6 Oe.

From the foregoing, it is considered that the value of the magnetichysteresis parameter becomes especially large in all of the first tofourth cases if the upper limit value of the applied field strengthreaches such a level that the hysteresis loop starting at a point on theinitial magnetization curve comes into contact with or protrudes fromthe major loop in the third and fourth cases.

To reduce the value of the magnetic hysteresis parameter in all of thefirst to fourth cases, the upper limit value of the applied fieldstrength is therefore preferably such that the hysteresis loop startingat a point on the initial magnetization curve makes no contact with themajor loop in the third and fourth cases. Specifically, the upper limitvalue of the applied field strength is preferably less than or equal to21.6 Oe.

From FIGS. 37 and 38, it is seen that the value of the magnetichysteresis parameter is especially small if the upper limit value of theapplied field strength is less than or equal to 17.4 Oe. The upper limitvalue of the applied field strength is therefore more preferably lessthan or equal to 17.4 Oe.

In the present embodiment, the upper limit value of the applied fieldstrength corresponds to the upper limit value of the variable range ofthe strength of the external magnetic field. The upper limit value ofthe variable range is preferably such that the hysteresis loop startingat a point on the initial magnetization curve makes no contact with themajor loop in the third and fourth cases. Specifically, the upper limitvalue of the variable range is preferably less than or equal to 21.6 Oe,more preferably less than or equal to 17.4 Oe. In other words, thevariable range is preferably a range not more than 21.6 Oe in absolutevalue, more preferably a range not more than 17.4 Oe in absolute value.

If the external magnetic field consists only of the detection-targetmagnetic field Hx and the variable range satisfies the foregoingpreferable condition, the coordinates (AHx, Mx) move within the regionenclosed by the major loop MALX, along a minor loop not in contact withthe major loop MALX. If the external magnetic field consists only of thedetection-target magnetic field Hy and the variable range satisfies theforegoing preferable condition, the coordinates (AHy, My) moves withinthe region enclosed by the major loop MALY, along a minor loop not incontact with the major loop MALY.

The upper limit value of the variable range of the strength of theexternal magnetic field may be determined by the following first methodor second method. The first method will be described first, withreference to FIG. 40. In FIG. 40, the horizontal axis represents theX-direction applied field strength AHx (Oe), and the vertical axisrepresents the X-direction magnetization-corresponding value Mx (emu).The definition of positive and negative values of the X-directionapplied field strength AHx and the definition of positive and negativevalues of the X-direction magnetization-corresponding value Mx are thesame as in FIG. 7. In FIG. 40, the curve denoted by the symbol MALXrepresents the major loop. The curve denoted by the symbol MCirepresents the initial magnetization curve in the first case.

In the first method, the initial magnetization curve MCi and the majorloop MALX are obtained by varying the X-direction applied field strengthAHx. Then, a tangent to the initial magnetization curve MCi at the pointof origin is determined, and an intersection of the tangent and themajor loop MALX is determined. In FIG. 40, the broken line denoted bythe symbol L is the tangent to the initial magnetization curve MCi atthe point of origin. The point denoted by the symbol P is theintersection of the tangent L and the major loop MALX. According to thefirst method, the X-direction applied field strength AHx at theintersection P is determined as the upper limit value of the variablerange. As shown in FIG. 40, the upper limit value determined by thefirst method is close to the preferable value (21.6 Oe) of the upperlimit value of the applied field strength obtained from the firstexperiment.

Next, the second method will be described with reference to FIG. 40. Inthe second method, a coercivity Hc obtained from the major loop MALX isdetermined as the upper limit value of the variable range. As shown inFIG. 40, the upper limit value determined by the second method is closeto the more preferable value (17.4 Oe) of the upper limit value of theapplied field strength obtained from the first experiment.

The effects of the magnetic sensor device 1 according to the presentembodiment will now be described. In the magnetic sensor device 1according to the present embodiment, when an external magnetic fieldincluding the detection-target magnetic field Hx is applied to themagnetic sensor 10, the external magnetic field is also applied to thesoft magnetic structure 40. When an external magnetic field includingthe detection-target magnetic field Hy is applied to the magnetic sensor20, the external magnetic field is also applied to the soft magneticstructure 40. When the soft magnetic structure 40 has a magnetization, amagnetic field based on the magnetization of the soft magnetic structure40 is applied to the magnetic sensors 10 and 20.

In the present embodiment, if the soft magnetic structure 40 has amagnetic hysteresis characteristic, the magnetic hysteresischaracteristic causes the detection values of the magnetic sensors 10and 20 to have a hysteresis characteristic, and can thus cause a drop inthe detection accuracy of the magnetic sensors 10 and 20. As describedabove, to minimize the drop in the detection accuracy of the magneticsensors 10 and 20 due to the magnetic hysteresis characteristic of thesoft magnetic structure 40, the values of the magnetic hysteresisparameters HPHx and HPHy are preferably as small as possible.

In the present embodiment, at least part of the soft magnetic structure40 has a stripe domain structure. If the variable range of the strengthof the external magnetic field is the foregoing preferable range, themagnetic hysteresis parameters HPHx and HPHy are smaller in value ascompared with a case where the soft magnetic structure 40 has no stripedomains so that almost the entire soft magnetic structure 40 has aclosure domain structure. This is because, in the stripe domainstructure, if the applied field strength is somewhat small, a change inthe magnetization-corresponding value in response to a change in theapplied field strength involves no movement of the magnetic walls W orno rotation of the stripes.

Consequently, according to the present embodiment, a drop in thedetection accuracy of the magnetic sensors 10 and 20 due to the magnetichysteresis characteristic of the soft magnetic structure 40 can bereduced as compared with the case where the soft magnetic structure 40has no stripe domains so that almost the entire soft magnetic structure40 has a closure domain structure. Such an effect will be referred to asa first effect of the magnetic sensor device 1. The first effect isexhibited noticeably if the variable range of the strength of theexternal magnetic field is the foregoing preferable range.

Next, a second effect of the magnetic sensor device 1 will be described.To begin with, the sensitivities of the magnetic sensors 10 and 20 willbe defined as follows. The sensitivity of the magnetic sensor 10 refersto the ratio of a change in the detection value Sx to an infinitesimalchange in the strength of the detection-target magnetic field Hx. Thesensitivity of the magnetic sensor 20 refers to the ratio of a change inthe detection value Sy to an infinitesimal change in the strength of thedetection-target magnetic field Hy. The sensitivity of the magneticsensor 10 can vary depending on the strength of the detection-targetmagnetic field Hx. A change in the sensitivity of the magnetic sensor 10in response to a change in the strength of the detection-target magneticfield Hx is preferably small. Similarly, the sensitivity of the magneticsensor 20 can vary depending on the strength of the detection-targetmagnetic field Hy. A change in the sensitivity of the magnetic sensor 20in response to a change in the strength of the detection-target magneticfield Hy is preferably small.

According to the present embodiment, if the variable range of thestrength of the external magnetic field is the foregoing desirablerange, a change in the sensitivity of the magnetic sensor 10 in responseto a change in the strength of the detection-target magnetic field Hxand a change in the sensitivity of the magnetic sensor 20 in response toa change in the strength of the detection-target magnetic field Hy aremade small. This is the second effect of the magnetic sensor device 1.The reason why the second effect can be obtained will be qualitativelydescribed below.

As described above, if the variable range of the strength of theexternal magnetic field is the foregoing preferable range, in theorthogonal coordinate system having two orthogonal axes for representingthe X-direction applied field strength AHx and the X-directionmagnetization-corresponding value Mx, the coordinates (AHx, Mx) movealong a minor loop not in contact with the major loop MALX. Here, theratio of a change in the X-direction magnetization-corresponding valueMx to an infinitesimal change in the X-direction applied field strengthAHx will be denoted by dMx/dAHx. The ratio dMx/dAHx corresponds to thegradient of the tangent to the minor loop at a point on the minor loop.

According to the present embodiment, when the soft magnetic structure 40has a magnetization, a magnetic field based on the magnetization of thesoft magnetic structure 40 is applied to the magnetic sensor 10. Achange in the ratio dMx/dAHx thus affects the sensitivity of themagnetic sensor 10. More specifically, the greater the change in theratio dMx/dAHx in response to a change in the strength of thedetection-target magnetic field Hx, the greater the change in thesensitivity of the magnetic sensor 10 in response to the change in thestrength of the detection-target magnetic field Hx.

In the present embodiment, the minor loop is closer to a straight lineon the whole as compared with the major loop MALX. If a point on theminor loop moves, the gradient of the tangent to the minor loop at thatpoint therefore does not change much. In other words, if the coordinates(AHx, Mx) move along the minor loop, the change in the ratio dMx/dAHx inresponse to a change in the strength of the detection-target magneticfield Hx is small. If the variable range of the strength of the externalmagnetic field is the foregoing preferable range, the change in thesensitivity of the magnetic sensor 10 in response to a change in thestrength of the detection-target magnetic field Hx is smaller ascompared with a case where the coordinates (AHx, Hx) move along themajor loop MALX.

Similarly, if the variable range of the strength of the externalmagnetic field is the foregoing preferable range, a change in thesensitivity of the magnetic sensor 20 in response to a change in thestrength of the detection-target magnetic field Hy is smaller ascompared with a case where the coordinates (AHy, My) move along themajor loop MALY.

Next, a description will be given of a relationship between the maximumabsolute value MHx of the X-direction applied field strength AHx and anX-direction sensitivity change parameter, which was examined on thebasis of the data on the first case obtained by the foregoing firstexperiment. The X-direction sensitivity change parameter willhereinafter be referred to as a parameter SVPx. The parameter SVPxindicates the magnitude of a change in the ratio dMx/dAHx when thecoordinates (AHx, Mx) move along a minor loop.

For each MHx value in the first experiment, the value of the parameterSVPx was determined in the following manner. First, data on thecoordinates (AHx, Mx) for an AHx of n Oe was extracted from the data onthe hysteresis loop for each MHx value, where n is an integer greaterthan −MHx and less than MHx. For each pair of adjacent coordinates onthe hysteresis loop with n values different by one, the absolute valueof the difference in Mx was then determined. The absolute value of thedifference in Mx corresponds to the ratio dMx/dAHx. A maximum value anda minimum value were then extracted from the absolute values of thedifferences in Mx of all the foregoing pairs, and a difference betweenthe maximum and minimum values was determined as the value of theparameter SVPx.

FIG. 41 is a characteristic chart showing the relationship between MHxand the parameter SVPx. In FIG. 41, the horizontal axis represents MHx(Oe), and the vertical axis represents the parameter SVPx (×10⁻³emu/Oe). In FIG. 41, the broken line denoted by the reference numeral 77indicates a position where MHx is 17.4 Oe. The broken line denoted bythe reference numeral 78 indicates a position where MHx is 21.6 Oe.

Although not shown in FIG. 41, the value of the parameter SVPx for anMHx of 250 Oe is approximately 0.51×10⁻³ emu/Oe. The value of theparameter SVPx for an MHx of 21.6 Oe is approximately 32% that of theparameter SVPx for an MHx of 250 Oe. The value of the parameter SVPx foran MHx of 17.4 Oe is approximately 11% that of the parameter SVPx for anMHx of 250 Oe.

From the foregoing results, it is seen that when the variable range ofthe strength of the external magnetic field is the foregoing preferablerange, the value of the parameter SVPx is sufficiently smaller than inthe case where the coordinates (AHx, Mx) move along the major loop MALX.From FIG. 41, it is seen that the value of the parameter SVPx isespecially small if MHx is less than or equal to 17.4 Oe.

It is clear that if a Y-direction sensitivity change parameter isdefined in the same manner as the X-direction sensitivity changeparameter, a relationship between MHy and the Y-direction sensitivitychange parameter in the second case is the same as the relationshipbetween MHx and the parameter SVPx in the first case. Furthermore, fromthe shapes of the minor loops shown in FIGS. 31 to 36, it is clear thatgiven the same MHx value, the value of the X-direction sensitivitychange parameter in the third case is smaller than that in the firstcase. Similarly, it is clear that given the same MHy value, the value ofthe Y-direction sensitivity change parameter in the fourth case issmaller than that in the second case.

Next, the results of a second experiment will be described. The secondexperiment studied the first effect of the magnetic sensor device 1according to the present embodiment. Prepared for the second experimentwere a plurality of samples of each of first to third examples and aplurality of samples of a comparative example. All of these are samplesof the magnetic sensor device 1. In the first to third examples, thesoft magnetic structure 40 includes the soft magnetic layer 41 and doesnot include the soft magnetic layer 43. In the first to third examples,the soft magnetic layer 41 of the soft magnetic structure 40 is squarein plane shape (the shape as viewed from above).

For the samples of the first to third examples, NiFe was used as thematerial of the soft magnetic layer 41. The Ni content was such that astripe domain structure was formed. The Ni content was increased inorder of the samples of the first example, the samples of the secondexample, and the samples of the third example. The samples of the firstto third examples were subjected to alternating-current demagnetizationin the X direction so that the stripe domain structure had a stripedirection parallel to the X direction.

The samples of the comparative example include a soft magnetic structureof the comparative example instead of the soft magnetic structure 40.The soft magnetic structure of the comparative example has the sameconfiguration as that of the soft magnetic structure 40 in the samplesof the first to third examples except the Ni content in the softmagnetic layer 41. In the samples of the comparative example, the Nicontent of the soft magnetic layer 41 was made lower than in the samplesof the first to third examples so that a closure domain structure wasformed in the entire soft magnetic layer 41 without application of anexternal magnetic field. Because of its formation method, the softmagnetic layer 41 in the samples of the comparative example had aninduced magnetic anisotropy with an easy axis of magnetization parallelto the X direction.

In the second experiment, the hysteresis parameters of the magneticsensors 10 and 20 defined as described previously and a hysteresisparameter of the magnetic sensor 30 were determined. Specifically, inthe second experiment, the hysteresis parameter of the magnetic sensor10 was determined from the detection value Sx obtained with the strengthof the detection-target magnetic field Hx varied after subjecting thesoft magnetic structure 40 to alternating-current demagnetization in theX direction. The hysteresis parameter of the magnetic sensor 20 wasdetermined from the detection value Sy obtained with the strength of thedetection-target magnetic field Hy varied after subjecting the softmagnetic structure 40 to alternating-current demagnetization in the Ydirection.

The hysteresis parameter of the magnetic sensor 30 was determined fromthe detection value Sz obtained with the strength of thedetection-target magnetic field Hz varied after subjecting the softmagnetic structure 40 to alternating-current demagnetization.Specifically, the hysteresis parameter of the magnetic sensor 30 is avalue determined as follows. The strength of the detection-targetmagnetic field Hz is set to a predetermined value Pz greater than 0,then decreased to −Pz, and then increased to 0. The detection value Szat which the strength of the detection-target magnetic field Hz reaches0 in the process of increasing is subtracted from the detection value Szat which the strength of the detection-target magnetic field Hz reaches0 in the process of decreasing. The resulting value is the hysteresisparameter of the magnetic sensor 30. In the second experiment, thedirection of the alternating-current demagnetization in measuring thehysteresis parameter of the magnetic sensor 30 was set to be parallel tothe direction of the output magnetic field component.

Hereinafter, the hysteresis parameter of the magnetic sensor 10 will bedenoted by the symbol HPSx. The hysteresis parameter of the magneticsensor 20 will be denoted by the symbol HPSy. The hysteresis parameterof the magnetic sensor 30 will be denoted by the symbol HPSz.

In the second experiment, the strengths of the external magnetic fieldand the detection-target magnetic fields Hx, Hy, and Hz were all variedwithout exceeding the preferable variable range of the strength of theexternal magnetic field. Specifically, in the second experiment, thehysteresis parameter HPSx was determined with the maximum absolute valuePx of the strength of the detection-target magnetic field Hx indetermining the hysteresis parameter HPSx set at 2 Oe, i.e., with thestrength of the detection-target magnetic field Hx varied within therange of −2 Oe to 2 Oe. In the second experiment, the potentialdifference between the output terminals Vx+ and Vx− was converted into anumerical value representing a magnetic field strength, and theresulting value was used as the detection value Sx. Hereinafter, Oe willbe used as the unit of the hysteresis parameter HPSx.

In the second experiment, the hysteresis parameter HPSy was determinedwith the maximum absolute value Py of the strength of thedetection-target magnetic field Hy in determining the hysteresisparameter HPSy set at 2 Oe, i.e., with the strength of thedetection-target magnetic field Hy varied within the range of −2 Oe to 2Oe. In the second experiment, the potential difference between theoutput terminals Vy+ and Vy− was converted into a numerical valuerepresenting a magnetic field strength, and the resulting value was usedas the detection value Sy. Hereinafter, Oe will be used as the unit ofthe hysteresis parameter HPSy.

In the second experiment, the hysteresis parameter HPSz was determinedwith the maximum absolute value Pz of the strength of thedetection-target magnetic field Hz in determining the hysteresisparameter HPSz set at 2 Oe, i.e., with the strength of thedetection-target magnetic field Hz varied within the range of −2 Oe to 2Oe. In the second experiment, the potential difference between theoutput terminals Vz+ and Vz− was converted into a numerical valuerepresenting a magnetic field strength, and the resulting value was usedas the detection value Sz. Hereinafter, Oe will be used as the unit ofthe hysteresis parameter HPSz.

FIGS. 42 to 44 are characteristic charts showing the experimentalresults. The vertical axis in FIG. 42 represents the hysteresisparameter HPSx (Oe). The vertical axis in FIG. 43 represents thehysteresis parameter HPSy (Oe). The vertical axis in FIG. 44 representsthe hysteresis parameter HPSz (Oe). In FIGS. 42 to 44, the referencesymbol CP represents the samples of the comparative example, and thereference symbols EX1, EX2, and EX3 represent the samples of the first,second, and third examples, respectively.

As shown in FIG. 42, the distributions of the hysteresis parameters HPSxof the samples EX1, EX2, and EX3 of the first to third examples arecloser to 0 than the distribution of the hysteresis parameters HPSx ofthe samples CP of the comparative example. It can thus be seen that thepresent embodiment is able to reduce a drop in the detection accuracy ofthe magnetic sensor 10 as compared with the case where the entire softmagnetic structure 40 has a closure domain structure.

Further, as shown in FIG. 43, the distributions of the hysteresisparameters HPSy of the samples EX1, EX2, and EX3 of the first to thirdexamples are closer to 0 than the distribution of the hysteresisparameters HPSy of the samples CP of the comparative example. It canthus be seen that the present embodiment is able to reduce a drop in thedetection accuracy of the magnetic sensor 20 as compared with the casewhere the entire soft magnetic structure 40 has a closure domainstructure.

As shown in FIG. 44, there was no significant difference between thedistributions of the hysteresis parameters HPSz of the samples EX1, EX2,and EX3 of the first to third examples and the distribution of thehysteresis parameters HPSz of the samples CP of the comparative example.

As shown in FIGS. 42 and 43, for the samples CP of the comparativeexample, the distribution of the hysteresis parameters HPSy is closer to0 than the distribution of the hysteresis parameters HPSx. The reason isthat in the samples CP of the comparative example, the magnetichysteresis parameter in the direction of the hard axis of magnetization,i.e., in a direction parallel to the Y direction, is small in value. Ifthe entire soft magnetic structure 40 has a closure domain structure andalso a uniaxial magnetic anisotropy, the magnetic hysteresis parameterof the soft magnetic structure 40 in the direction of the hard axis ofmagnetization becomes small in value. On the other hand, the magnetichysteresis parameter of the soft magnetic structure 40 in the directionof the easy axis of magnetization becomes large in value. Accordingly,as shown in FIG. 42, the hysteresis parameters HPSx of the samples CP ofthe comparative example are large. Thus, if the entire soft magneticstructure 40 has a closure domain structure, a drop in the detectionaccuracy of both of the magnetic sensors 10 and 20 could not beprevented by providing the soft magnetic structure 40 with a uniaxialmagnetic anisotropy.

In contrast, in the first to third examples EX1, EX2, and EX3, both thehysteresis parameters HPSx and HPSy are small. Such a result indicatesthat according to the present embodiment, a drop in the detectionaccuracy of both of the magnetic sensors 10 and 20 can be prevented bythe soft magnetic structure 40 having a stripe domain structure.

The present invention is not limited to the foregoing embodiment, andvarious modifications may be made thereto. The first magnetic sensor andthe soft magnetic structure of the present invention may be any onesthat satisfy the requirements of the appended claims. For example, thesoft magnetic structure is not limited to one having the functionrelating to the magnetic sensor 30 such as the magnetic field converter42 and the soft magnetic layers 41 and 43 of the embodiment, but may beone having a different function, or may be a structure that simplysatisfies the requirements of the appended claims.

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. Thus, it is to beunderstood that, within the scope of the appended claims and equivalentsthereof, the invention may be practiced in other embodiments than theforegoing most preferable embodiment.

What is claimed is:
 1. A magnetic sensor device comprising: a firstmagnetic sensor for generating a first detection value corresponding toa first detection-target magnetic field; and a soft magnetic structureformed of a soft magnetic material, wherein the first magnetic sensorand the soft magnetic structure are configured so that when the softmagnetic structure has a magnetization, a magnetic field based on themagnetization of the soft magnetic structure is applied to the firstmagnetic sensor, and at least part of the soft magnetic structure has astripe domain structure.
 2. The magnetic sensor device according toclaim 1, further comprising a second magnetic sensor for generating asecond detection value corresponding to a second detection-targetmagnetic field, wherein the first detection-target magnetic field is acomponent of an external magnetic field and is in a direction parallelto a first direction, the second detection-target magnetic field is acomponent of the external magnetic field and is in a direction parallelto a second direction, and the soft magnetic structure is arranged notto overlap the first magnetic sensor but to overlap the second magneticsensor as viewed in a direction parallel to the second direction.
 3. Themagnetic sensor device according to claim 2, wherein the soft magneticstructure includes a magnetic field converter configured to receive thesecond detection-target magnetic field and output an output magneticfield component that is in a direction intersecting the seconddirection, the output magnetic field component has a strength having acorrespondence with a strength of the second detection-target magneticfield, and the second magnetic sensor is configured to detect thestrength of the output magnetic field component.
 4. The magnetic sensordevice according to claim 3, wherein the soft magnetic structure furtherincludes at least one soft magnetic layer.
 5. The magnetic sensor deviceaccording to claim 2, wherein the first direction and the seconddirection are orthogonal to each other.
 6. The magnetic sensor deviceaccording to claim 2, further comprising a third magnetic sensor forgenerating a third detection value corresponding to a thirddetection-target magnetic field, wherein the third detection-targetmagnetic field is a component of the external magnetic field and is in adirection parallel to a third direction, and the third magnetic sensorand the soft magnetic structure are configured so that when the softmagnetic structure has a magnetization, a magnetic field based on themagnetization of the soft magnetic structure is applied to the thirdmagnetic sensor.
 7. The magnetic sensor device according to claim 6,wherein the first to third directions are orthogonal to each other. 8.The magnetic sensor device according to claim 1, wherein the firstmagnetic sensor and the soft magnetic structure are configured so thatwhen an external magnetic field including the first detection-targetmagnetic field is applied to the first magnetic sensor, the externalmagnetic field is also applied to the soft magnetic structure, theexternal magnetic field has a strength varying within a predeterminedvariable range, and in an orthogonal coordinate system having twoorthogonal axes for representing an applied field strength and amagnetization-corresponding value, coordinates representing the appliedfield strength and the magnetization-corresponding value move within aregion enclosed by a major loop as the strength of the external magneticfield varies within the predetermined variable range, where the appliedfield strength is a strength of a magnetic field applied to the softmagnetic structure in a direction parallel to a predetermined direction,the magnetization-corresponding value is a value corresponding to acomponent of the magnetization of the soft magnetic structure, thecomponent being in the direction parallel to the predetermineddirection, and the major loop is, among loops traced by a path of thecoordinates representing the applied field strength and themagnetization-corresponding value in the orthogonal coordinate system asthe applied field strength is varied, a loop that is the largest interms of area of the region enclosed by the loop.
 9. The magnetic sensordevice according to claim 8, wherein the predetermined variable range isa range not more than 21.6 Oe in absolute value.